on the old trucks (99-02) the Z06 cam is supposed to be good for 50hp with the stock intake and exhaust.

 

Thats being very optimistic there, 25-30 is more like reality, a nice gain for having stock idle qualities.

The better way to go is to just buy the pacesetter off road y-pipe and a couple of high flow aftermarket cats, and then install the headers and y-pipe and then just cut out a space for the cat on each side and weld them in, piece of cake and you will have alot better flow than trying to butcher up the stock y-pipe and will be better in the end.