Hey Devin, how about the Mamiya 645 1000s (does anyone still sell the 1/500th-limited non-s?) option? Lens info relevant to Super/Pro too, but my A$0.02:
I'd love a 80/1.9 too but the two 80/2.8s that I had were both fine standard lenses, the N versions are "newer" plasticky feeling ones with generally cheaper helicoids I think, they match the later 80s cameras (Pro/Super) visually, optically there is debate about whether they changed (if so only coatings): had one of those and one of the older "Sekor C" ones - go the old school. Most people who get the 1.9 seem to have buyers remorse or, at best "it's better than my 2.8 but not by enough".
An alternative might be the 55mm (I have an N version, not sure if there was a 70s original), which I find quite capable. Since giving away my 80 on my spare body (wedding 'tog payment!) it's been my usual lens, and I'm happy with its handling, view, and negatives. In fact I think my favourite 645 shots were from that lens. It's a bit longer but not much heavier (if at all) than the 80, and mine was a good deal cheaper at the time.
For metered prism finders, the PD finder seems the one to get, and mine is plenty accurate, pattern I like etc. Bit on the bulky side and can be hard to find for less than the camera+lens from time to time though! Plain finder's sleek enough to stick in a consumer-grade camcorder pouch, and not that dim (though I've never Hasselbled to compare). There exists a waist level finder if you want the TLR feels but they're rare, though suuuper slim/light (wow, a few metal flaps and springs fold flat? amazing! 🙄). No idea how this compares to the later cameras, but the plain prism is definitely lower profile than the Pro style.
Finally: the strap mushrooms are not Hassy sized, but I recently learned they are (allegedly) Pentax (6x7 & 67) sized - confirmation anyone? Ebay knows only of the latter 😉. Again, might have changed later, I doubt it.
You don't even want to change lenses, do you really need interchangeable film backs? The old cameras are tough as...
Oh, and an afterthought: they're very tinkerable to my eyes: I think I've found a service manual somewhere online (never used it) and things like the focus screen height, prism standoff etc. are all obvious and doable with minimal disassembly. Mine was a school photographer's workhorse and that makes sense looking at how it's built. Magazine seals might well be an issue as mentioned (they were on my spare body) but 10 minutes with a foam strip kit off the 'bay sorts it.
Not light but.