1963 Chevy Nova oil pressure

Do an engine flush don't work probable causes could be excessive engine bearing clearances or pressure relief valve

This is a 2 year old GM Crate engine with 3500 miles on it, In a 1963 SS Nova Convertible, Problem started about two weeks ago, Seems like the oil pressure went from an average of 35 - 45 lbs on the highway to 5 - 10 lbs of pressure at 65 MPH, again engine seems to run fine just very low pressure. Tested it with a mechanical oil gauge under the hood, Same reading!!changed the fittings, used a different guage (New AutoMeter gauge) What's up??? Headed to Columbus GoodGuys July 9 10,11 .any ideas???????????

Is this from the mechanical gauge or the oil gauge indicator-try replacing the gauge.

Any engine knocking noises of any type-maybe we should try the oil pressure sending unit and see what happens