52: I have not converted a welder, this is basic power engineering stuff I learned over the years. The Yanmar parts will be easy to get if You use the same engine that was used in John Deer equipment, they made the entire tractor for JD in the past, maybe still do. Kubota engines are good too. My preference is a pushrod engine, I would stay away from timing belt driven overhead cam engines, if You do end up with one, change the timing belt and the idler bearing according to the manufacturers schedule.