Rear End??

[melman109]

Can someone school me on rear end differentials? I need to know what gears or gear ratio to use. I have a 68 Camaro, and I want to have a 9" ford fab for it. I went to a few shops and they all told me that I have a choice of gears to use but I don't know anything about gears or how to determine how many I need. Can someone help me?........If it helps I will not be putting this car on the track and I plan on running a 500 hp engine with a 700r4 tranny.. Thanks!