X2--Use cracking pressure as the base for your high speed.
The exhaust temp. sounds pretty close
After looking at this with a clear head. Get rid of the pressure in the oil pan and the RPM's will come. It's like dynamics, EX: lock your fingers together and pull with either arm, resisting with the other. The stronger arm will win. Same thing with you engine, the top side wins but not without resistence. I don't know the vacuum system you have but if it started out with 12 inches vacuum and ended up at 20/25 lbs. pressure in the pan before it blew the intake gasket, there are some serious issues with the collection system, being plugged or a breather problem plugging up or filling up. i sure with you would have tried header evac system on the dyno. I also think you have another 50 HP once you get rid of pressure in the oil pan, and as many RPM's as you want to run.
JMO.
Zip.