With just a valve job/chamber cut, narrowing the valve guide boss and short turn work those heads should go 305cfm at .500 lift! It sounds like that's what's holding you back the most.
The srp 220157/157 pistons should only have 17cc dish...you may have measured wrong?
What's the chamber volume? Are you sure about your measurments??
When ported correctly, that head will have a large chamber...more like 68-71cc. So some milling would should have been done or they didn't open the chamber up any.
Cam is too small for that power level.