Sometime back in the "80s we replaced the SM 420 in the 57 6400 with one from a school bus and did an in-frame refresh with rings, bearings and rear seal on the 261. This pto unit would not fit so we installed the old one and retro-fitted an operating mechanism. It has been sitting on a shelf in the shop ever since, wrapped in an old shirt. Have no idea what it came off of.Jethro.