Hi Mark,
The solid deck machine has the earlier cast iron clutch body and the twin railer has the later revised version being made out of die cast, this one has the hidden captive cotter pin. Neither unit is as good as the current spec that has two set screws that pin the clutch body to the PTO shaft in two places 90 degrees to each other and thus eliminate any ability for the body to move, thus less flogged out clutch bodies now. BTW if you have a correctly maintained first version cast iron bodied clutch then that is the very best unit made but as we all know that all companies try to trim the fat in production costs and the clutch was a major fat trimming area on the machines as they evolved.
Cheers,
BB
