Should be able to find a service manual pretty easy for this model, ebay, TSC, basically any generic farm store should have or be able to get you one. Whats the problem with the pto,, slips or wont stop perhaps? Its been many years but slips could be as easy as an adjustment and wont stop is usually warped discs, fairly easy job to replace the discs. I think a 55 series was more a 70's machine, the 50 series was 60s if I remember. Been 20 or so yrs since I worked on one, I remember some of the basics but none of the details.