If he were just putting in the cam, the stock spring would be fine but not with the rockers. The LS6 springs should be fine with that cam/rocker setup so no need to go out an buy a set of 918s. I bought all the gaskets for the swap and didnt use them. I figure I will just hold on to them till I do a bigger cam in the future. The pn are:
12559271 - Water pump gaskets, (you will need 2 of them)
12558013 - Front cover gasket
12561244 - Front seal
12557840 - Crank bolt
If you are carefull taking everything apart you should be able to reuse all you gaskets but I would go ahead and change the crankbolt since it is a stretch bolt.