What kind of c-4? what gear ratios in the tranny? What does he want to do with the car street/strip or track only? Then there are alot more variables after that, but I ran a set of 3:73s behind an old truck c-4 (dont even know what ratios in the thing) and that was a wild and fun ride.
Use this site to figure out what gear he wants depends on his crusing speed, crusing rpm, and tire size that he wants. http://www.richmondgear.com/101032.html