Rear Differential help

probably shouldve asked this on the tranny/rear end board, but seems like theres a lil more action here.

im building up a 440 in my 69' RR, and i need help selecting/finding a rear end. since im gonna building the engine to 600+ HP an torque i was thinking of going with a chrysler 9-1/4".

what do you guys recommend? and where can i find a new one online or one in decent shape. also what is the difference between running a 3.90 gear and a 4.10? and the difference between c clip and a dana then obviously the shape of them. sorry for all the questions but im completely lost when it comes to differentials.
Author: Nightmare