Your best bet for horsepower gains, is to stroke it. But if you want to just go bigger bore, I have a set of 66mm jugs and pistons, mild port, that are getting ready to go up for sale soon. Only have about 20 hours on them, if that. I'm getting a 68mm cub. I am also debating on getting rid of my 4mm longrod crank, and going with a 10mm crank. Money is what's holding me back there.