I have a 1970 Plymouth with a 440 six pack and 58,000 miles. I changed oil today and used Fram oil filter with 10w40 Castrol, I had been using Wix filters and 20w50 oil. I started the engine and it built oil pressure, went for a 15 minute drive and had it to the floor a few times.
I noticed there was no oil pressure and the lifters were rattling. I had the car towed home, removed the oil filter and it did not have oil in it. I removed the valve covers and it checked all of the push rods and they appear to be fine. Drained the oil, installed a new Mopar filter and filled it with fresh 10w40. The oil did not appear to have anything that looked like bearing material.
Still no oil pressure.

Good news. I could not build any oil pressure when I tried priming the engine with a drill through the distributor. I kept hearing gurgling and hissing under the intake manifold. After 2 days I thought about trying to drink through a straw with a hole in it and decided to pull the oil pan. The oil pick up tube was cracked where it threads into the block and broke off when I touched it.
A trip to the auto parts store for 2 pan gaskets and a $17.50 pick up tube and the bird is running. Thanks to everyone for their advise.
Thanks