It is kinda odd, Most of the F-bodies came without a computer (but that percentage was growing sharply by '80), while most (almost all) of the M-bodies came with a computer (only a handful left without a computer, except for those destined for outside of USA).
The three-wire oil pressure switch wiring is different from the single wire oil pressure switch, which he has. If he tapped into his oil pressure switch wiring, his dash oil light would be on pretty much anytime the car is turned on (see attached), or more exactly, anytime his choke heater is turned on.
That said, I do agree with you on the early '80's cars (and newer), but not in his case.