431 combo will react like a 446 just a couple hundred rpm higher. I would use small port heads for the street because you're torque peak will still be well over 4000. For a bracket motor I might go to the next size heads but The rpm would go up about 1000. B1 heads may have problems with a 4.280 bore? At any rate the b1 head wouldn't start working till somewhere around 5000 rpm and would make peak power at over 8000 rpm. 383 blocks aren't very strong from what I hear.