Hi mikeo, welcome to Outdoorking.
Those SB45s look very promising in the picture, and worth far more than $50 each - especially the 20". Nevertheless they will naturally need some work to get them working to their full potential. The 17" in particular should not be operated until you have done this, since it looks as if the clutch has slid along the PTO and may now be in contact with the crankcase cover.
If you wish you can post some close-up pictures of the machines and get comments on some critical features, such as their originality, the remaining life of reels and bedknives, and the condition of chains and sprockets. They also need to be checked carefully for engine mounting rail cracks near the bolts.
Much of the trouble - aside from normal wear - that SB45s give is associated with the clutch between the Power Take-Off and the drive shaft. It is usually necessary to pay careful attention to this area and in all probability overhaul it, before putting these machines back into normal service. Unfortunately there may have already been previous neglect, which often results in cracked engine mounting rails. Such faults can be fixed, albeit with some difficulty, but prevention is far better than cure.
