[Sirrotica]

Just read this and was wondering how a piece of old lifter went through the pickup screen and survived the gears in the pump to end up in the filter. If it in fact went through the pump without locking it up, or breaking the driveshaft, or roll pin in the distributor drive gear (doubtful). If it did the pump could be trashed internally causing low oil pressure. A retainer clip is about the biggest thing I can envision going through the pump and screen.

I'd be leaning towards a stuck pressure relief ball myself especially if there's broken parts floating around in the oil pan, but only guessing at best, only one sure way to find out what is going on and that involves a lot of work. No mechanic in a can is going to fix this one.