Donald Tanner,
That's a CW36 model snowthrower. It came out just after the BB36 which was for the Originals. The CW36 was brought out for the 70/100 and after narrow frame tractors. Although that perticular one has some vertical holes in the mounting frame that mine doesn't have. They could align with the Original front frame holes. If you have an O' with front PTO clutch it could work. The BB36 had its own PTO engagement system since most O's didn't have front PTO, just the raw pulley.
Looks to be in nice original condition. I'd get it if I were you!