7. The factory roller lifters use plastic guide trays to keep lifters from spinning in place, yet make assembly quick. The head gasket is also made of multi layers of thin metal for a simple yet effective seal. The LS2 we built used the factory 243 casting aluminum heads outfitted with Manley intake valves, factory GM exhaust valves, and 190-psi valve springs. These heads are known to flow great and are held in place with 10 head bolts with five extra small bolts.