[91whiteghost]

Victor Jr heads ( part no.77189) have 60 cc chambers with 2.05 intake, 1.60 exhaust, same for no 77189 which is a complete head with vale springs and retainers. part no's 77389, 77399 are 70cc chambers , same size valves.preformer rpm heads are 60cc chambers and either 1.90 valves no's 60229 or 2.02 valves no.s 60259,69,602519. piston to valve clearance has to do with the cam profile9 straight up , advanced , retarded etc.) head gasket thickness , piston to deck clearance and depth of valve notch. I assume the pistons are not for a twisted wedge head or something similar. hope these specs help