Hey mike, guess what! just bought a close ratio gearbox of a guy in the States and he had a set of genuine Honda pistons.
The good news is they are the same as the aftermarket ones I got, so work on the motor can go ahead.
I have everything to do it now apart from the correct carb, just missed one on ebay a few nights ago
Maybe another one will turn up by the time it's ready to go into the chasis.
Sam.