The first series has spur type gears. The SM420 has helical gears. The pto is different in the two. The bolt pattern on the clutch housing is different also. However, the clutch housing to the engine is the same. Swapping everything leads to clutch linkage and rear engine problems, but it can be done. I would first look for a pto on an old farm truck. About all that ever goes bad on old pto's is the seals. If you can live with the old sliding gear transmission, it certainly be much easier putting a pto on it. Another possibility is converting to 12 volt and using an electric hydraulic pump like lift gates use.