Gee, I wasn't aware that any of the Oliver's ever used single action hydraulics. I could be wrong, though. We sold a 1550 gas and if I remember correctly we sold the feller a 3 bottom semi-mounted plow. Don't recall his ever having any problems. Allis Chalmers used single action hydraulics in the D-series tractors and maybe even into the 190/190XT's and they used fully mounted and semi-mounted plows on them.