Dave...
Mine was held down the same way,had the same head gasket and had less timing(24 degrees) when I was trying tog et the small Garrett GT3788R Stage 3 over the top and drive pressures like what your seeing caused the gasket to fail.I did mine with simular drive pressure readings when I was acting like a fool chasing my buddies built twin chargered WRX STi.I'd say it would be worth your time to get that vented out and get rid of the exhaust wall your seeing,it may free up a little top end but I am convinced that it will not tear the wall completely down.
I really do not think that fuel pressure is one of your issues.With what your seeing unloaded the numbers you laid down are not going to change with a spring change in the pump.When I dynoed mine back earlier last spring the pump on mine was a 150/180(180gph that was failing)FASS that was at 24psi and pulled down to 7psi under load and when it was dynoed last fall it was a 180/200 FASS(200gph) and the pressure was at 50psi at idle and under load as it never changed.As a matter of fact neither pressure or volume made any difference in the overall number mine ran and the charts can be laid on top of each other they are so close to the same.
Congrats on the nice runs BTW.