Maybe I'm a bit confused and I don't want to go back into all the old posts (lazy shize I know), but here's a quick quation for the techo boffins:
Standard piston diameter for the RD07 = 81mm with 72mm stroke (742cc and 9:1 compression) http://www.xrv.org.uk/forums/africa-...fications.html
If I remember correctly, maximum oversize Honda pistons (got a set at home, but too lazy to go rip them out and measure them now) = 81.5mm
I've got some JE high-compressy pistons in at the moment and am pretty sure they are 82mm. And Honda Hawk 650 pistons (3mm oversize) = AT 750 pistons (1mm oversize). That's around 760cc.
How big can you go without cutting the crankcase? What's involved with cutting the crankcase?