Couple of things come to mind:
1: missing gasket on valve cover breather, this will leak all over the cover and be thrown by air pressure all over the front of the engine and seep to the oil sender downstream.
2: Possible high crankcase pressure, with engine running and breather off, feel opening with hand, should be pretty neutral not greatly positive. These are the symptoms you are showing
3. I would change the oil pressure sending unit
4. I would not hesitate on replacing the throttle cable, get the last series with the built in spring, you will also need the carb bracket for that or trim the cable ends by about a quarter inch each.
5. If you are using a PCValve, check it and the vacuum circuit.
6. See number 4
7. IMHO
Good luck
Angelo
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