Now that I want to scan the pictures, I can only find 1 of the 3 I had. Here it is:
If early to mid sixties is what you are trying to replicate, go with a Chrys. 8 3/4 or one of those Olds style diffs. from the Revell, Anglia. The quick change from the Revell, Austin Gasser would also be fine. The way that you describe the chassis indicates that this car may be more dragster than roadster. If so, don't use any rear suspension or traction devices. The diff. housing would have been most likely been bolted directly to the frame rails.
If you could post a pic of a similar car, I might be of more help.
Thanks for all the help.