Replacing the oil pump should not be a problem. If the engine had good oil pressure before, and no main bearing knocks, I wouldn't touch them. You can take each cap off, have a look and then replace it. If there are ridges or lines on the crank, your bearings will be worn in a matching manner. If you do decide to put a new set in, you will have to let the crank down enough to clear the dowels, and that will mean removing the transmission and front timing cover.
