I've finally comitted to a motor: D&D ES-15A-6. This motor is heavier (62lbs), a little more expensive and much larger (~12.5" long) than the Etek-RT that I was originally thinking of using. I'm sure the Etek would have done the job, but in the end D&D's reputation for quality & customer support was the deciding factor.
If you have done any browsing of EV projects, you know it's fairly common to have problems with ordering parts from the cheapest source. I've spent enough time in the manufacturing arena to know some of the pitfalls in supplier selection. Up front cost is only part of the equation.
With the motor specified (and on it's way!!) I'd better get serious and figure out how to mount it. I see a lot of guys use the NEMA face mount by welding a plate to the frame, but that is not going to work on El Gixxer. Welding is not an option for this project, so the trick for me is using the existing rear motor mounts on the frame.
One advantage the D&D has over cheaper motors is that it can be mounted using the case as a structural member. The motor even comes with case bracket for mounting on flat surfaces. My idea is to use some 1.5" x .75" aluminum stock to make a couple of mouting struts. Once the motor arrives, I will make a wood model to try it out.