[Keithc8]

I do not know how much power you are looking for but a nice 331C.I. with the KC 165 heads, hydraulic roler around 224/232 and a Performaer RPM intake should make a easy 425 to 435HP and I would think about the same torque.
If you have to run the header that you are talking about anything bigger or with a better head would be limited anyway. The exhaust on these cars kills more power than most people know. I have people buy big heads and then stick small tube headers on them covering part of the exhaust opening and the pipe size will not the exhaust flow as it should. The header pipe size and bolt pattern need to be considered when getting headers. This will in turn have a lot to do with the engine size and other things. It all has to work together.
I think you will be surprised at how well the engine will work for you.

Good luck, Keith Craft