Oil pump replacement?

I have the truck listed above, it belonged to my dad. It sat in his yard for several years due to it having a blown head gasket. He told me to fix it if I wanted it and get it out of his yard, which I did, and it was running good, when it left his yard, I drove it home no issues it had great oil pressure. The next day I drove it maybe 2 or 3 miles and it suddenly lost oil pressure. I had some seafoam in the crank case the night before right before I left my pops. I went to drain the oil out after losing pressure and when I removed the plug it went drip, drip, and a big chunky skinny goo ball plopped out and then the oil started to drain. Could maybe that oil pump not been able to pump that thick goo and just lost prime? Could I just need to prime it again and if so, how would I go about doing that? Do I need to remove it from the truck to do so? Any help or advice I can get is appreciated.