You aren't going to want to buy heads, unless you know what pistons you have, otherwise compression ratio is unknown. I would start by giving your motor a few more degrees of ignition timing, 28 is good for a really hot smallblock with very efficient combustion chambers, 34 might be more to your motor's liking.
You could get what you want buying ONLY: heads, pistons, cam, lifters, rockers, (and gaskets,
oil pump, timing chain while you're in there) But by then, you might as well spring the extra few bucks for a stroker crank and some block machining, cause you are allready almost completely redoing the whole motor.
If you don't want to spend so much money, new cam and lifters( and valvesprings) will make it a different motor, maybe not much faster, but different.