I'm not a small block guy but I run the B1 original heads and have run them on a 470 BB. That motor made around 800HP. I would think the Koffel heads should do the same on your combo with an average port job, 360+ intake flow, and 32* of timing. I am also sure someone else here is more qualified to talk about B1/BA MC's and small block power numbers. The MPH and ET look right for 10.0's and 131 and 650HP. If you go to a taller gear, 4.10's or something, it will slow down IMO.