As breadcrumbs for those who might follow, here are some details of the vendor and product choices I made that might help someone else.
I went with a mid-drive for its sophistication and class as well as efficiency. It has better hill-climbing ability than a hub motor and more versatility than any direct-drive. Among choices, I went with the TongSheng TSDZ2 because it's a Pedal Assist System; the torque system simply ADDS torque when you add torque, and therefore it doesn't turn your bike into a moped, which means I get the exercise I want / need. I went with the 48v / 500W because I'm a big guy (6' 3") with a heavy bike and will be carrying luggage, so power is required.
I went with the VLCD5 version (instead of Xh-18) because of my handle bars and because it has accessory options the Xh-18 doesn't have.
I bought from these people because of price and because others reported success. Mine was $290:
http://www.auto-ebike.com/index.php?mai ... ts_id=1802
While ESL was a problem, I got what I ordered in good time. I would order again and just know their English is poor and communications may be frustrating at times.
I didn't get what I wanted, but it's good advice to get as much energy storage (expressed as Ah, amp-hours) as you can find and afford because packs degrade because charges may not be complete, because you may change plans or use more than intended, and, many battery management systems and motor control systems cut out at around 3v (per cell). There are many versions of the Lithium-ion battery out there, the 18650 is by far the most popular and lowest price per Ah. As of this writing, the LG brand MJ1 is the highest storage on the market, but it can be out of stock and is counterfeited often, but even with the MJ1, it appears to get its extra capacity via deep-discharge - the only one whose specification sheet I read that officially slated it to go to 2.5V and survive! So, if the battery management system or motor controller cuts you out at 3V, you have excess capacity you cannot ever use, though it very well may help battery longevity to not deeply discharge as far as they claim.
Only go with a reputable vendor - ask around! I went with this pack with the 33G cells due to price and availability and this vendor due to recommendations. Looks like it was a good call:
https://em3ev.com/shop/preditor-l-47v-8 ... e-battery/
I've studied the specifications for at least five different 18650 cells and unfortunately, they all vary in terms of what their official charging requirements are. Perhaps more unfortunately, they all require altering charge voltage and current during the charge cycle. If you keep the voltage at what some less technical people call 100% you WILL over-charge virtually every cell. That voltage is 4.2v per cell. If instead you drop it as the manufacturer calls for as the battery approaches full, you'll get a properly full cell at 4.1v. And, if you don't also attend to charge current as it fills, you can also damage the cells, so voltage is not the whole story. To get around this, many battery chargers give you a so-called "80%" and / or "90%" option at the flick of a switch. Do Not Be Fooled. What's happening is making up for having a stupid charger by simply lowering the peak voltage below 4.2. This increases charging time with the attempted tradeoff of battery longevity.
Note also that many people talk as if 4.2v (per cell) is the "fully charged" voltage - IT IS NOT! 4.2v is the CHARGING voltage. And, cells have some capacitance so they'll look like 4.2v when freshly (and fully) charged but that's what's known as the "float" voltage and it will fairly quickly dissipate. Lithium ion batteries, by their chemistry, are completely full at 4.1v. This is very clear from the literature. They all have this trait.
As noted above, different versions of the 18650 have different charging criteria. TYPICAL characteristic for charging requires 4.2 v to charge when deeply discharged and then later in the charging cycle the voltage should be dropped to 4.1v per cell. Again, this is all very clear from the specification sheets for the various cells - and again, they're not all identical in this regard. If you don't have a charger that charges according to YOUR cell's manufacturer's directions, then use the 80% or 90% strategy as a stupid-charger way of not over-charging as a stupid-charger otherwise will do.
And all this is why I'm investing in this charger:
http://www.ebikes.ca/shop/electric-bicy ... iator.html
Not cheap, but great technology. You can create your own charging profiles if you want! Read the literature! Worth The Money (so long as it doesn't fail prematurely, etc).
Drivetrain: Gearing / Chain / Wheels / Hubs
Know what the issues are for YOUR motor system by reading up owner reports! ... The TSDZ2 has two pertinent issues: 1) it's known to wipe out "the blue gear" with too much power applied in too low a gear, and 2) It's known that the pedal-assist system drops out (ie stops assisting) beyond about 90 Pedal-RPM. You should DO THE MATH to figure out what that means to you, given your wheels diameter, chainrings (front gears) and rear gearing. To help, I created this Microsoft Excel / OpenOffice Calc format spreadsheet - download and tailor to meet YOUR needs:
Know also that the TSDZ2 has a 5 X 110 BCD sizing for the front ring and comes with a 42T. My pupa started with a 40 and a 52T. 42T works out close enough to 40 as to be reasonably identical but it's not a reasonable substitute for both gears. So, I am adding a steel 52T - it's not mounted yet, I have to do the offset work, etc, however I have confidence I'll get it working. If you're doing this, you'll need the right mounting hardware and I recommend a type that has female hex sockets for tightening instead of the "classic" inept slots it comes with. The TSDZ2 has an aluminum plate with the 42T mounted on the inboard side and it's a highly inboard offset gear as well. On the outboard side it has a chain guard. There's not much room on the inboard side for another gear, but MAYBE they can coexist on the left side - I'll find out!
In the rear, my bike measured 122mm between the mounting anchors for the rear axle, and it originally runs the "freewheel" style rear gearing - old school. As there are no modern freewheels in a gearing that works for me AND from a reliable vendor (Shimano stopped production in the mid 1990s), and as there are no cassette systems available on pre-made 27" rims, I'm making my own to get the rear gearing that works for me. The hard part is finding a rear axle. I went with a Shimano Nexave FH-T300 Silent Clutch Rear Free Hub 130mm 36H 7-Speed Silver. I will spread the frame out from 122mm to 130mm using a hydraulic ram intended for automotive bodywork repair - 8mm is just a bit under 3/8" (6mm is nearly exactly 1/4"), so each side will see less than 3/16" change - not much. This rear hub is available on ebay right now for $19.99 with free delivery. Note that I chose this particular one because it's the narrowest free hub, gives me at least 7 gears and its spoke count is 36 (the H in 36H stands for hole!), which matches the rims I found, from Sta-Tru Wheel. I found these new on Amazon for less than $100 the pair, delivered, in aluminum with quick release. Now I just have to "re-lace" the new spindle into the rear wheel. Here's that axle:
http://www.ebay.com/itm/Shimano-Nexave- ... D100282%26
For rear gears, I'm going with Shimano again, the CS-HG41-7 It has 11-28T gearing. From slowest, here's the comparison:
Stock: 28, 24, 20, 17, 14
HG41-7: 28, 24, 21, 18, 15, 13, 11
As you can see, the tallest two are identical and the new one goes a LOT taller, with the middle spread a little better, just one tooth different. In theory this gives me a 34.2 MPH top speed with assist at 90 Pedal-RPM. Not bad!
Here's a link to the one I got:
http://www.ebay.com/itm/Shimano-CS-HG41 ... 1474192371
Of course, I bought a set of new tires, tubes, and spoke liners - interestingly, the same brand, size and color as this bike had when new!
... The tires / tubes:
http://www.ebay.com/itm/2-Pack-Kenda-K3 ... 2714820472
And, I bought a new chain, even though I may not need one - also got a chain wear measurement tool. Here are the chain and chainring mounting hardware:
https://www.amazon.com/gp/product/B001G ... UTF8&psc=1
https://www.amazon.com/gp/product/B00N3 ... UTF8&psc=1
In my view, this is required for the bike; a "traditional" kickstand! They show it with a ruler - should work on a 27" wheel.
https://www.amazon.com/gp/product/B06XV ... UTF8&psc=1
I got a Hand Throttle I intend to use as an emergency only item, in case I'm injured and can't pedal. I got it from AliExpress.com. Find it here - sans brake cut-out switches:
https://www.aliexpress.com/item/36V-48V ... 7a90fc92c3
$060.00 Shipping the TSDZ2 from Hong Kong
$318.00 Battery: 47V (13S4P) Preditor L"47V" 12.4Ah (13S4P-33G)
$077.30 Shipping for the battery
$318.00 Charger: Grin Cycle Satiator Charger, "48v" version, with accessories
$026.80 Shipping for the charger
$019.95 Rear axle w free hub & quick disconnects - Shimano Nexave FH-T300 130mm 36H
$018.35 Cassette gears - Shimano CS-HG41-7 11-28T
$045.84 Front Wheel - Sta-Tru silver alloy 27" X 1.25", quick disconnect
$048.90 Rear Wheel - Sta-Tru silver alloy 27" X 1.25", quick disconnect (freewheel type)
$032.59 Tires, tubes, rim strips w shipping: 2-Pack Kenda K35 Gumwall 27x1-1/4"
$015.00 Chainring, 5 X 110 BCD, steel
$009.50 Chainring bolt set, TruVativ, in steel, hex both sides, with spacers
$029.99 Kickstand (see link above)
$019.79 Thumb-Throttle (see above)
$1330.01 Grand Total (so far!)
(NOT DONE HERE, just saving to ensure I don't lose all my writing!)