There's a square or rectangular plate bolted onto the side of the case on all the SM-420's I've seen, that's where the PTO mounts. You'll need an assortments of gaskets of different thickness to adjust the backlash of the drive gear (very important from a reliability and noise standpoint), and depending on the function of the PTO you choose to use, it might be necessary to install an adapter between the case and the PTO with an idler gear in it. What sort of accessory do you intend to power?
Jerry

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