Hy C10 - C90 Bill, medium duty P.T.O., straight cut gears, early 50s most likely. Not enough gears to be a two speed or reversible. I have 27 P.T.O.s here and none have that same code, I have been searching for an old P.T.O. application catalogue for 35 years, next time I'm at the Pacific Northwest Truck Museum in Brooks Oregon I'm going to look through their stuff. The "C" on the tag might stand for Clark, but that is just a wild guess. Good luck tracking down the info and let us know if you do.
