543

Standard port heads and intake. I figured the 543 would be choked off by not enough head.

All engines get choked off by something. You didn't say how much power you want to make or how fast you want to go so it is hard to answer your question. A 543 with SR heads, a cast intake and a 4150 carb will probably have peak power at 5500 rpm. If that works for you then go for it. If you want peak power at 7000 rpm then you'll need to change parts.