It sounds like its a used engine, so I would probly stick with the dino oil. If its not a roller, and it sounds like its not, I would either get an ""off-road"" oil, or use an additive with zinc in it. Most new oils have low/no zinc, which helps emissions in new cars, but the zinc helps protect in high load areas, particularly flat tappet cams. Or you could use full synthetic high-mileage oil which has seal conditioners added so that it wont leak, but will likely still lack the zinc.