speedaire 3Z745A-2 pump overhaul

I want to overhaul the pump, (R158C), on this 1988 unit. I can find parts lists for very similar pumps but none for this one which has two breathers. One from the crankcase to the atmosphere at the end of what resembles an oil dipstick tube abd the other from the cylinder head to the crankcase via 1/4" tubing. I will need rings, a gasket set and valves, With respect to the valves, why would I need to replace the valve plates assuming the old ones are serviceable? Thanks so much for any advice/ assistance you can offer.