76- 4oo engine Can i get 500-550HP stock exhaust

Its the stock exhaust manifolds that will hold it back the most. if you cant get it out, you cant get it in.

Ditch them and run headers, then your home free.

We have found 40hp 0n a 340 just by using a better HEADER, I would bet a set of manifolds would have cost that 340 100hp.