Im far from expert but we used a stock 621 bell housing, truck flywheel (NFW-1050) and standard clutch (RAM-88764) with 26 splines with a TKO600 onto an LS3.
For hydraulics we used an actuator set up from Speedway Motors and our master cylinder plate set up.
http://www.shop.meanstreetsperforman...-BCBPKIT69.htm
For race you might want to go with a SFI bell and centerforce clutch.
flywheel info 2001-2005 Silverado 1500 BaseV8 - 4.8L vin V 294ci - MFI GAS OHV