I think the pressure relief should be set at 57 so it looks right to me. If those are "hot" figures then I believe that is real good. I don't have a mechanical gauge on mine but the stock electric gauge reads close to those same numbers and I know my engine is very tired! I don't think I have ever seen a bottom end that is any more overbuilt than the 226-H. That is a tough little motor.
51, you can be very happy with your oil pressure. I have a freshly rebuilt 59A that has good start up pressure (50 lbs.) . At prolonged idle it drops to 7 psi. I know a knowledgable ex flathead racer and he says that if you have any kind of pressure at all at idle (5-10 lbs.) it is adequate. He,s given me much valuable info over the last few years and has not steered me wrong yet. Steve