Thanks Trigger,
I did do some searching and came up with 70mm as std, problem is the engine builder if he can’t get hold of the pistons he leaves you to find them so I’m kind of doing this homework and he’ll rebore to suit. I will have a look at the pistons to see what size they are as well, the engine code is cb500E XXXXXXX, but I’m hoping that I can getaway with just new rings.....well that is the plan anyway!. I’ll give IMD a call and see what they can do, so thanks for that.