IMO you are really cranking for unported 906s. Compression helps. But more headflow should really add power with everything else you've got going on, the heads are the weak point for sure. Stock valves or 2.14/1.81s?

Also, assuming you've got something like 6 cc valve notches I think 12.6:1 compression is a high estimate. You'd need a 65 CC combustion chamber which on a 906 would be milled until the step pad was gone, although people have done that.