Mmm cheers for the info, iv taken the head off the 1000 chain drive and slid it onto the 850 and the studds were ok, iv a gs1100 barrels and cv head which im probably puttin g on the 1000 to then use bandit carbs, iv 750,850, 1000, and 1100 engines here so will have a play n see just what will fit on what, iv just picked up a head stamped s4 today so i think iv 4,5 6,7,8 now so will check and post the findings, i know the 1000 pistons have bigger pins so thats a no no swap to the smaller engines