on the older carb'd motors you had to pull the heads on the ls blocks you dont have too, do what ian said and you'll be fine.
Since when did you have to pull the heads? Valve covers , loosen rocker arms , remover push rods , intake , remove lifters. left a few steps out but you get the point.
'02 GMC RCStepSide 4.8 , Thumpr Cam , 3200 Stall , OBX LTs , MSD Wires , TrueTrac , 4.10s , 3/5 Drop , bolt in traction bars by LSX Powersports , EFI Live tune by LSX Powersports
15.2 @ 90 , 2.3 60' (Only mods at this time , LTs)