top tip: thats a OEM piston - it came out of something - research the online fiche I posted up for the 2 cyl bikes
I would suggest a GPz305, TS250 , estrella 250 all these will give plenty cc x 4
What about the new Ninja 400R - that could be a 600+ conversion !
Another contender is a ZZR500 , these were made for the states , stroke might be suprisingly the same - do your homework folks !
As for a copper head gasket - simples, standard gasket laid over copper sheet , scribe. Centre cylinder bores and scribe to new value, cut.
No wear values are given on this kit , it was never fitted yet bought for a challange WTF ???
Is it a straight fit or do you need the base gasket increased ?
No scraper ring is race use so it has been raced.
Race big bore is difficult hence toecutter doing his thing but street big bore just takes some research and a machine shop - there is only a limit when they can't take out your block anymore to accept sleeves.
I can do a 600cc conversion on my ZRX400 using ZZR parts but need to use 5 base gaskets or find a ZZR500 crank. I could also have falcon make custom crank pins (conrods) to suit my application but for money & time spent and a marginal seat height difference a ZRX1100 will give me more so why do it, less weight I guess but then I need to up suspension & brakes so all told - get the 1100
However a 500cc conversion on the ZXR is plausable - the chassis can handle it , machine shop time here is expensive though but that shouldn't stop you - those are ART slugs and in production so NOT rare !
MM!