I just found this shot on my phone, from that fateful ride.
The frame is back from the welder with a foot of 1/8" wall tubing up through the bottom. Wire brush, sandpaper, and rattle can red paint waiting for me to find some ambition.
The wheelbase is 74", as I recall. All the specs are here.
The Avid BB-7 is working great. I am about halfway through the first set of stock brake pads. The brakes get far less use on this bike than on my pedal bikes, as I use regen for all but the last few feet of a stop, and just a tap of regen before entering fast curves.
If I was going to do anything now, I would make a new frame from scratch. It would be all bolted together, like my mid-drive. I'd use 2" x 5" x .125" x 54" for the main tube, 1 1/2" x 3" x .125" x 18" for the chainstays. I'd put a hole through the top front corner of the big tube for this bottom bracket.
https://www.amazon.com/Sunlite-Threadle ... B016QRQTU0
It would require a 3/8" thick aluminum spacer ring on either side to bring it out to ~68 mm width. Twelve inches back, C-C, I'd put a hole going through vertically, for a press in 1 1/8" threadless headset. With an 1 1/8" headset, I could buy a fork with disc brake tabs, and save wear on the rim of my carbon front wheel. The rear chainstays would be flush with the bottom of the main tube, and overlapping by 6". There would be two 6 mm bolts, on 3" spacing, holding the chainstays on. There would be 2" aluminum spacers, on either side, between the chainstays and main tube, to get the ~ 150 mm spacing for the motor. The dropouts would be 1 1/4" x 2 3/4" x 7" bars of aluminum. They would slide 4" up into the chainstays, and have threaded 4 mm holes, on 2" centers, for holding them in the chainstays. At the outer ends there would be a 14 mm hole in each one, for the motor axle. The motor torque would be handled by 8 mm flat point set screws. A hole would be drilled and tapped up the end of the dropout, through the hole, and into the opposite side. This allows a setscrew on either side of the hole, extending out to touch the axle flats. The inner one is set to touch the axle before final assembly. The outer, second one is tightened down after assembly. I used a smaller version of this setup for the torque arm on my mid-drive hub motor. Tabs would be added to theses blocks for hanging the rear derailleur, and brake caliper. Once installed on the axle with those big nuts, I wouldn't need to carry a 22 mm wrench for fixing flats. A hex wrench, for the 4 mm button head bolts, would allow the wheel, derailleur, and brake assembly to come off in one piece. The wheelbase would be just under 60", with the seat and battery right in the center of the wheelbase. The weight of the rear hub motor would put the weight distribution at about 45/55 front/rear.
There would be aluminum spacers/tubes inside the main frame and chainstays, to take compressive loads at the bottom bracket, headset, and chainstay bolts. It wouldn't be very pretty, but it would be simple and cheap, and could be anodized to help the looks.