ORIGINAL: flywilly

YS 61AR and the 'ABC' version of the Hanno special (MKI or MKII)

I believe you could put the AR version in the earlier Longstroke, but I'd check the porting in the case to make sure, of course a little work with a Dremel tool would work, too

FYI - the stock YS piston/sleeve is listed as AAC, however the 'C' is not chrome, but does last longer than the Nickasil used by OS. If you have a new OS/YS and a new replacement piston/sleeve from Performance Specialties or me (both built by Henry Nelson) then I'd replace the stock with the Nelson parts and save the originals for a rebuild later (maybe never) or to rebuild another engine. The stock OS liner typically lasts 300-500 flights (sometimes longer if the engine isn't run too hard) before performance degrades due to 'peeling'.

-Flywilly