if you bore over you will need new pistons and rings.. there are alot of options, just depends on how much you want to go over. Honda made overbore sizes 1 - 4. These were in .25mm increments.. so 61.25, 61.50, 61.75, and 62.0mm. You can find these oem pistons on ebay. Ken from Cycle exchange also makes a cast overbore setup for about $200. Includes everything. You can also go alot bigger than 62. You can go to about 66mm w/o having to resleave the jugs. If you want, you can go up to 70mm but that requires alot of work and alot of money for machine work... you will also destroy any sandcast jugs that you use.
There are other honda pistons that people have used in the past. Something like a 360 twin piston (some modifications necessary) and I think the CBX pistons from the 6 cyclinder are 64mm pistons that will work as well (I think that is about a 812cc)
Weisco makes an forged 836 kit for about $450-500. Its pretty nice but it isint cheap. 836 is a 65mm bore.
Ken from cycleX also makes a cast 65.5mm (850 kit) that is only $250 and that includes everything.
I am currently searching for a larger piston that I can use in my engine. There is likely one out there in a car or different motorcycle that should bolt right up.
Things to think about. Boring should be about $10 per hole at a machine shop. This rate should be about the same reguardless of how much over you go (.25mm - 4mm). Be sure and buy the pistons before you get the machine work done. Any reputable shop will measure each piston and bore accordingly to get precision tolorances.
If you go with a size other than the stock honda overbore pistons, you will need a head gasket to match the bore size. Also be sure and get the correct compression ratio that you want. More compression = more power. If you are going after lots of power go with forged pistons but my guess is that is not your goal here.
