the b&m stage II kit works pretty well, i used a TCI streetfighter valvebody in mine this go-round so it has a similar kit already installed.

have them use alto red eagle clutches and kolene steels when assembling the tranny - the price different in parts is NOT that much more and they will hold up to any future power ALOT better. also invest in a better servo (round thing on the side of the tranny) it will help reduce the 2-3 shift flareup which is a weak link in the C4's. lastly, a stock stall would be ok, but you could get something like a "saturday night special" converter which is just a couple hundred rpm higher than stock (these are about the same price as a stock reconditioned converter)