Hey check with Mike Shortline.
He has a good stash of 90 piston and ring sets.
* 1978 ATC 90/180 Pauter PJ1 / Springer "Team BAPP" Bike *
* 1980 ATC 110/180 "Danny's Machine Works" 3D Sprint Dune Bike *
* Nicholson 500 Race Bike *
* HPATC Yamaha RD350 "Big Moe" Trike *