i dont know much about autos so thats were you auto freaks come into play. i $600 to start rebuilding my c6 transmission. what's a good rebuild kit? torque converter? valve body? shift kit? what else to build up a bad ass transmission?
why C6? That thing is a friggin boat anchor that sucks up power.
Unless you plan on running better than 10's, a C4 should be fine. I know of at least 1 c4 running 8's in a tube chassis car.
unless you have a 460 i would not use it, it is a great tranny but very heavy and it use 60 hp to turn. all you really need to do is replace the clutches and all the broken pieces and install some torrington bearings instead of the cheap HP robbing bushings. that will cut the parasitic hp robbing down some. put a small shift kit in it and an optional manual valvebody in it, then go with a 2600 stall. are you sure you got the right c6 because there are different kinds. they made them for small blocks and different ones for big blocks. since the c6 has an integral bell housing which means the tranny housing is one piece, you will have to have a SB c6 if you still are using a 5.0 or 5.8. i would still do a c4 or c5 though.