I am rebuilding a pre 2011 gx390 that has a long skirt piston with 2.0mm rings. By chance i have a 2011 & later "smart engine" piston ,short skirt with 1.2mm slim rings. both measure the same at the skirt. Has anyone ever swapped these out? does the newer piston retro fit back to the older engine? again before we start i have mic'd the skirt & the cylinder is good i just dont want to but another piston & ring if these , that i may never use will work?