Report "I recently rebuilt a 1960's model 350 Jawa 2 stroke twin engine using a later model crankshaft assembly,with needle roller small end bearings.But the pistons still use the three cast iron rings.My question is,is there an even later model piston I could use with the same piston dimensions ( 58- 59 mm bore)but having two rings,perhaps narrower chrome rings or similar? Ken"