Rear drum brakes

My ego? Buddy you're the one arguing about a car that was 40 years old when you bought it.
I mean, I saw a Fiero with a Lambo kit at a wrecking yard once, but I'm not gonna say it came that way from the factory. Lots of things happen. Drag racers switched disk cars to drums back in the '70's because they thought the pad knock-back would slow them down. Guys pull disk brakes and later model K frame's from donors and roll their early suspension underneath before then send it to the scrapper. Happens all the time with the '73+ cars.
I admit that you do have some knowledge but you aren't old enough to have seen these cars when they were new. For that matter, neither was I...at least I wasn't old enough to work on them then. You can't argue what you didn't see.
My point....
There were some strange things done back then.
Sure, the scenario you presented above is plausible and likely. I still say to have seen as many 9" drum brake cars as I used to see adds at least some doubt to your absolutes.