The Magnums are are a good 4 stroke engine, and are very dependable. They are a little underpowered compared to the likes of Saito or YS, but are almost identicle to O.S in most aspects. I have Magnums, and Saitos, and have no complaints with either. The Matt Cap 580 with a Magnum 70 4 stroke would be a pretty nice combination in my opinion. I have a 72 Saito on my GP Cap 232 of almost the same size as the 580, and I would have no complaints using a Magnum 70 in its place. I would lose just a touch of power, but it would still perform very well.