well it looks like GR650 pistons are rarer than hens teeth so what was the options. remember we are in the UK and this is a budget build so after market pistons are out. so the question is does anyone know of an alternative.
Suzuki sells GS500 pistons that are .5mm or 1mm larger in diameter although that's negligible when you think about it... I think it's 13ccs at best and it's nothing compared to the 3mm difference in GR650 pistons.