I'm assuming that it's a V8 because you said "heads". Is the rear end a 9" or 8"? If you build an engine with alot of power, you should have the 9". With a 3-speed tranny the highest I would go would be 3.55 if you don't plan much highway driving, but 3.25 would good for both highway and the street. Hopefully your friend labeled all the parts so you know what they are and where the go! Good luck.