Do a compression test to check the top end. If you haven't done this before, try youtube. Seems there's lots of instructional videos there. Is there blue smoke? How about blowby? Remove the oil filler cap while it's running. Does it blow out oil and have pressure? Now thread in a mechanical oil pressure gauge in place of the oil pressure light sender. With it warmed up, see what the OP is. The factory service manual will have the specs, but without looking, 15 psi at idle should be okay. I have one truck that idles at about 5 psi and it still has some life in it..... Oh, and welcome to the fridge group. And you happened to get the best year , 1959!