Hi Ben, I found your thread yesterday and have just finished reading through it. I'm curoius:
* Why are you using the S10 transmission? It might be cheaper and less complicated to find a used Mercedes trans. and weld up new mounting brackets than to make an adapter plate w/ your current setup. Btw, jack had some cool info on how to make the adapter plates in his thread, here:
Project Land Yacht (BMW 5-series EV conversion) - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com
* It sounds like you're going to be using a DC motor. When you are not supplying power to the motor, are there any limitations on how fast you can/should turn it under engine power? I think I read that you were sizing the motor to enable you to start the truck rolling with it attached direct drive (behind the transmission). I wonder if, when you have the trans in 5th gear and you're running the truck down the freeway at 70mph, if the motor could see damage or premature wear to it's brushes from the huge rpms.
This is a cool project! I'll definitely be following along. I'd like to do something similar with my truck, but had been looking at getting the 4wd version of my transmission and attaching the motor via the transfer case. If I could find an electronic transfer case, then I could disconnect the motor above it's relevant speed, and reconnect it on the fly... If you find out that you do have to be careful w/ the bearings in your motor, then this might be an alternative mounting point for you, rather than behind the trans.