You shouldn't be having any trouble, C6's for FE's were used behind millions of pickups. Internally, in general, they are all basically the same whether SB, FE, 460. It's the bellhousing pattern, cast into the case of course, that is different. There are minor differences between all of them as far as number of clutches and steels used and seals for things like the servo piston. The kits generally have extra seals. Extra clutch frictions can be purchased if the kit doesn't have enough. Where are you trying to purchase a kit from?