Installed the battery box and a 20T pinion and let it rip. Now we are talking. It has some speed now and the rearend squats hard. Surprisingly the trans held up just fine, but I wasn't getting all stupid with it either because it's not mine and I know how to respect 6S power. Of all things, the slipper gave me problems because the nut kept loosening, getting the steel spur so hot that it could have been used as a branding iron. I put some Loctite on it so that should be a non-issue. I'm gonna try a 22T pinion, box it up and give it back to the owner. Thanks for all the help and info guys, it was appreciated.

Final configuration. It's tight, but it all fits under the narrow Proline 50 Chevy P/U body.