Re: Disc Brake Size
Wait, do you mean the size of the rotors or the booster? As far as I know, all of the "stock-type" front disc kits use 11" rotors (OK, I lied -- some use 10.5" rotors and metric calipers).
BUT, most list multiple different power brake boosters. If we're talking power boosters, 11" is the "stock" size and works well, but might not clear tall valve covers on some applications (big block?). Smaller 9" boosters clear tall valve covers, but don't provide as much assist.
So let's back everything up a bit...
-- What size wheels are you running (15", 14", ???)
-- What are you looking for in a disc conversion (better brakes? better LOOKING brakes?, "bling", ...)
-- What engine do you have (big block? small block? I6?)