If you really want more power out of this car, you dont have alot of choices. The B18 head isn't going to fit with just "a little toying", you're talking custom machine work on the head and creating a custom head gasket.

If you just want more power than what the carb motor has, then just go with a Fuel Injected 88-91 prelude motor. That will involve changing out the wiring harness/ECU and getting all the sensors and everything, though you can keep your tranny and even the engine block (just use the fuel injected head). You'd need to change over to Fuel Injection anyways if you wanted to swap the B18 head on or even with an H22 swap.