The tapping starts after running the truck about 20 miles down the freeway at about 50-55 miles an hour. Could need an oil change. I haven't driven the truck too much on the freeway. After getting off the freeway and driving local roads, the tapping stops. Sounds like it is coming from the top portion of the engine. The oil gage started to go a bit haywire. At low idle it would go to between 10-15 and after excellation go to 30. Don't know if the gauge is off or not.

I restored a 64 Ford F250 recently and had the original engine rebuilt in that truck and after driving the good ole CA freeway the engine starting tapping too. I took the truck back to the mechanic and he said the top portion of the engine wasn't getting enough engine oil needed for that kind of engine stress. He did something to have more engine oil directed to the the engine and the truck has never done that again.

Guess the old 51 needs to make a trip to the doctors.
I just thought it was weird that the tapping only occurs during freeway driving. I just bought the truck several months ago and was told the engine was rebuilt recently. Was also told that the engine was a 67 to 72 model.
I will change the oil and take a test run but I think it's time for a thorough going over at the doctors if nothing more than for my peace of mind.
D