Of course, neither of my local dealers stock the parts, but the dealer 85 miles away have six of each...
I cleaned the oil pressure sending unit last night with contact cleaner, dried up the connections, and started her up. The OP light went out, then began to slowly creep back on at idle. I looked under the hood, and could see a stream of fresh oil coming from under the oil filter housing assembly. It was too late in the evening to begin dismantling, but that's definitely a prime candidate. Guess I know what I'll be doing next week...