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

The only way I see this happening is NoS or some kind of forced induction.

Its a tall order. 550hp, quite(as in smooth idle for sleeper affect), stock exhaust manifolds, low money output, pump gas. I think the best you can hope for is 450-475 with what your asking for. Im not saying 550 is not possible, but it will cost a ton to get, like the top runners in the FAST class. Those engines rock, but cost a ton.

SBM trans will not bolt up to a BBM.