I just bought a 1931 Ford Town Sedan with a 1974 Ford Truck 302 engine. This engine was rebuilt about 4000 miles ago. I am getting low oil pressure readings so I replaced the electric gauge with a mechanical one. At start, the pressure is 40 psi cold. When driving it gradually goes down to 20-25 psi. At idle when warm, it is 5-10 psi at best. no unsaul sounds,

Here is what I am going to try:
1 change the oil filter (there is plenty of oil) Can a plugged filter cause this?
2. The oil pan was repleced by the former owner with a chrome pan. Could it be smaller than needed?
3. clean and/or Replace the oil pump
4 (I hope not) pull the engine and check all of the bearing clearances.

Any other ideas?? Thanks