79 kz400 aftermarket/oversize pistons

Hey guys getting into the swing of things aND tearing stuff down for winter. Ive searched and searched and am unable to find aftermarket or oversize pistons for a 79 kz400. Ha's anybody had an luck different pistons that fit without modification to the head? Or does anybody know where to source .020 pistons?? Thanks in advanced guys. Will post pictures of both motors when I get a chance