I placed a bet on the Dimension adjustable-angle stem for $28, and I think it's a winner. It has a wide adjustable angle, but that can also be increased quite easily with a file, by cutting back the stops a little if needed.
http://www.niagaracycle.com/index.php?c ... =2a&page=8
The three lengths listed are 95mm, 110mm, and 125mm, which is the measurement from the center of the quill-clamp (QC) hole to the center of the handlebar-clamp hole. The QC (on the left) has an Inside Diameter (ID) of 1-1/8". You can mate the 1-1/8" QC to the common 27.2 seat-post with a $7 shim from "Problem Solvers", part # ST0214 / 27.2mm-28.6mm (or, also a tin can and a pair of shears! the wall thickness is only 0.7mm/0.027")
The center of the QC to the center of the pivot is 30mm on all three choices, so the three arm lengths (center to center) are 65mm, 80mm, and 95mm. I am listing this, so that those who are interested can mock up a paper dummy before purchase.
Concerning the arm length, it has a hollow center with an oval cross-section that is 30.7mm tall X 27.8mm wide. If someone needed a longer arm, you could cut its length in two, and then epoxy (JB-Weld / Devcon) a section of very common 27.2mm seat-post to any length you needed.
The hinge-bolt is 6mm X 1.00, Standard-Thread (std), 30mm long (5mm hex-wrench)
The two QC-bolts are 6mm X 1.00 (std), 18mm long (5mm hex-wrench)
The four handlebar-clamp bolts are 5mm X .80 (std), 15mm (4mm hex-wrench)
The bar clamp is available in several diameters. This first one I chose to try is 31.8mm, the other optional diameter I am interested in is the 25.4mm (1.0-inch). By ordering a stem with a handlebar diameter in one of these two sizes, you can use a very common aluminum or steel seat-post in the clamp as a cross-bar ($12 new, 31.8mm here:)
http://www.niagaracycle.com/product_inf ... _id=600559
edit: added the Kalloy Uno 95mm. The Kalloy stem-arm also has a hollow center through its length, with a circular-cross section of 0.912-inch diameter, and a 62mm length from center-to-center. Its QC length is 33mm CTC. Bolts are the same as the Dimension stem.
I want to try using two seat-tube clamps (set on the two ends of the cross-bar) that are thick aluminum with flat sides like the one pictured below, from Dimension. These clamps are $6 each, and this model is available in the 31.8mm ID that I am interested in. They are thick enough that the bolt-hole can be bored out to accept a 7mm, or 5/16-inch diameter bolt (if needed).
Niagara Cycle carries the 31.8mm unit, and JensonUSA also carries it. Jenson claims to have a USA warehouse in California, so ordering from them may be faster for US customers. Here's a link to a similar unit that also has flat/parallel sides from Sunlite, but with the smaller 25.4mm/1.0" ID :
http://www.niagaracycle.com/product_inf ... s_id=11832
http://www.bestbikebmx.com/catalog/prod ... 6938e80a32
By swapping in a longer bolt, the clamp can have protruding threads that insert into the top-plate of my drive. If you want to use a larger diameter bolt in order to source a long enough bolt locally, the bolt-head may not fit inside the stock recess, so be aware the outer width of the clamp is 40mm (1.57-inch). The seat-tube clamping-bolt is a 6mm X 1.00 (std), 34mm long, using a 5mm hex-wrench.
As a side-note, this very strong clamp would also be useful for attaching a DIY rear cargo rack to a bike, (while still performing the duty of a seat-tube clamp), perhaps bored-out slightly to use 1/4-inch all-thread rod, so threads extend on both sides.
http://www.niagaracycle.com/product_inf ... _id=417672
http://www.jensonusa.com/store/product/ ... AID=214987
I also bought this $8 lever-clamp by Origin-8, and I am very happy with the strength, quality, and the very long handle. I plan to attach the drive to the seat-post and remove the whole drive/seat/post all together on a regular basis.
http://www.niagaracycle.com/product_inf ... _id=431881
Some parts finally arrived, and I am pleased! It took 11 days from Niagara Cycle, most parts were marked “Taiwan". Quality and strength looks very good.