72 318 Scamp. Low oil pressure 1 minute after startup.

Thanks everyone for all of the ideas kn the problem. The scraping sound is the flex plate. It has a chunk out of and it's hitting the edge of the bellhousing. I will post a picture here. I changed the oil and filter and put in dino 10-30. Oil pressure starts off at about 50 psi and the stays there for about a minute. Maybe it was 40 seconds. Then it drops to 5 ... maybe so I shut it down.

I am going to do a compression test today and a maybe cylinder leakage test too.
Do the oil priming test sounds like a ingenious idea! I have never heard of this before. When would I get the oil priming tool? Or just get a old distributor from the junkyard and hook my drill on to that?

Also when I pull the pan I will look for sludge, loose pickup, clogged pickup, bad oil pump/shaft and bearing clearances.

Is there anything else that I should check?

Also what weight/type oil do you normally run in a old 318. I live in Montana and it gets cold here but unless it's an emergency I won't be driving it in the winter. Here is a picture of my thermometer on March 9th. It was -29 F. It bottomed out at -31 about and hour later!

Thanks again everyone.