AJ's Opinion; what size SBM do I need
That depends. Cam timing has as much or more effect on RPM than air flow does. When I switched from W2 to W5 heads, I kept the shift RPM the same but with the W5 heads I used 14 degrees LESS duration on the intake side and 18 degrees LESS duration on the exhaust side.
Still made power at the same RPM. It made more HP but the RPM a curve was the same.
