G'Day Clevo, well if it was me I'd go the Wiseco big bore route, good quality and a bit more "grunt" won't hurt, but otherwise, I bought new standard rings from Cyclex or Z1 (can't remember) for 40 bucks for all 4 pistons and they look fine.
Are you going to get Mike Rieck to do your head? He did one for me, and it's fantastic, apart from the magic porting and bigger stainless steel valves, he has them blasted to remove all the old crud, machines the gasket surface flat, installs all new guides and seals, so when it comes back you'd swear it was new, and it costs less than a new (if you can find one) OEM head.
You don't have to install a massive cam like I did, but a mild Megacycle cam with the headwork and a big bore kit will make your bike feel like a two wheeled ballistic missile!