Sprockets are really the next cost effective step in this process. Some people will tell you to ditch the head gasket for a little more compression. I disagree. If there are any irregularities in the mating surfaces of the head and jug, then hot, corrosive exhaust gasses will leak out and eventually "burn" the aluminum head. Not to mention, you will actually lose compression in that case. Puch head gaskets can be obtained in different thicknesses. You can get the thinnest one from a knowledgable dealer. Sorry, I don't know the actual specs. This is a smarter way to go for a little more compression.
Other things to do are to experiment with intake manifolds and carb jetting. Some Pucks have round intake ports on the jug, some have square ports. Puch makes both sqaure and round port manifolds as well. I have seen bikes with mismatched jugs and manifolds from the factory and this robs power. The manifolds come in varying throat sizes too. Best thing is to find a place where you can sift through a box of old, used manifolds iuntil you match one up.