Thanks a lot guys for the tips it seems there is enough different things about the Magnum I better get a book about them. I have talked to a local Mopar engine builder and he told me they run really strong but the factory Magnum heads are a little too small for a 408 engine to make good power. The Edelbrock Magnum heads are designed to use small block Chevy which is a plus because you can get a decent set of rockers without spending $600-800.
My buddy wants to get into the low 12's or high 11's with a smallblock in a 71 Road Runner and from what I've been reading it's possible with a 408 and some good heads.
Gus