Jim is correct you have to be satisfied with 180 ish hp with a SOHC engine but if you go with an older 4 cam with Atom ECU and cam you might get over 200, and elastically 220hp but you can't do any more without being disengenous to yourself and others. Words from a ralley racing engine builder north of the 49th.
A turbo WRX engine setup would be more than enough for our PCCA cars for sure and can be found for a lot less money used.
Marty has a GT 240hp ish and is quite pleased.
Update: I ran an exercise once to get pricing on a new engine with 200hp and more in a N/A and I had heard some say you could get 220-240hp and my local guy subie tech was telling me that it was impossible to get it and even 220 he felt they were exaggerating their results and says to me those numbers are reported in Cali.
In the end he says to me a small turbo can get you there for little money compared to a new NA especially if we find a good used low mileage engine. Still in the planning stage.