I unbolted the rack and pinion so I could remove the steering shaft and get the oil pump out without removing the engine.
The hex tip of the oil pump drive was still in the oil pump, as expected. There was no debris in the oil pump.
The pump turns smoothly by hand (with a hex rod inserted).
I measured the outer gear to body clearance and it was fine at 0.009" (brass feeler gage). Spec should be less than 0.014"
The tip clearance between inner and outer rotors is within spec (less than 0.010"). It was less than 0.006"

Could an engine backfire cause this with stiff valve springs? The day it happened I tried using the MSD start ignition retard, and the engine didn't like it. But then it started the next try (and no oil pressure).