Re: Oiling issues on the 65 F 100
This is an FE, right.
You need to remove the rocker arm assemblies, completely dis-assemble and clean the components and replace what is defective. You them must verify the oil delivery bores in the cylinder heads are clean and pumping oil.
Reassemble, adjust as to FORD directions and enjoy.
The engine is simply old and sludged.
If you have the system (early) where oil is also delivered to the rocker arm tips through drilled push-rods, those passages have to be clean also.
Of course, this is assuming correct oil pressure and the pickup screen is not covered with sludge.
The above posted information is in my opinion only. It may contain copy and paste material(s). Your opinion(s) and mileage may vary.