Tom, be sure that the sender is mounted in the back of a 351-C block. There's a second oil pressure port just over the fuel pump mount in front that, if used will give higher oil pressure readings that won't agree with anyone else's engine.
Don't expect too much from the stock oil gauge. I once assembled eight (8) different senders of the same brand and tried them one at a time on my engine. I got six (6) different readings from 5 to 15 psi apart. I added a mechanical gauge on a tee fitting with the sender; now if I want to know the actual psi, I get out and look at that mechanical gauge. The dash gauge only I use to be sure the engine is running. The stock water temp gauge is almost as bad.