xtof,
if you really want to go for 56.5mm pistons (500cc), you will need to fit different connecting rods, that is rods with a 15mm small end, also I would reccomend new cylinder liners because if you machine the standard liners they become very thin, on top of that, if you install new liners you will need to machine the engine cases to accept them, then of course, the base gasket won't fit and you will need to alter it.
So as you can see it all gets quite complicated compared to using a 460cc kit which has 13mm small ends and only requires the original liners to be bored out to suit.
Obviously it won't produce quite the same power as the five hundred conversion but is still very acceptable.Depends on how far you want to go !
Try Kevin Mullen @ ksm enterprises, or Kevin Bidgood @TTR400, both these guys can supply this kit and both are very knowledgeable and helpful.
Dave