Here's a pretty good site for finding different dimensions. I agree that it would be neat to get everything from one donor car, but don't sacrifice a good rear end just because it's an 8" Ford (for instance). The 8" will hold up to a Chevy V8 better than most of the wimpy Chevrolet rears you'll find in the smaller cars.
http://www.teufert.net/other/rear%20...dimensions.htm