if you are staying NA you wont be looking at huge bhp figures but bolting a turbo to a closed deck ej22 would sort that. However as its a strong block you could look at maximising the NA potential by blueprinting (lightening, balancing, porting, flowing, etc) and raising the compression, the gain in BHP wont be huge but the driveability and response will be there.
Running some lumpier cams will increase your top end rush.
Obviously the more you can do yourself will keep the costs down and you will get peace of mind knowing what has been done when by whom