So, after another search attempt, here's what i found:
Model 83, 84, and 85 all seem to be 3v models.
The B-101 seems to be the closest. I did try searching for a B-100, and I found an archive for an old eBay listing that has a bell-front instrument, but it looked like a 3-valve from the thumbnail, and the listing on eBay is long gone to confirm.
So, my last ditch effort was just google the actual description: "holton bell front 4 valves".
I got a hit: A Holton B-300.
Googled Holton B-300, and the first site showed up (
https://texashorntrader.com/shop/ols/pr ... t-baritone, and I'll attach pics for the sake of archiving it, and a cached eBay description which is no longer on the site: "Holton B300 4 Valve Bell Front Baritone. Parts Only"
It might not be the right model, but it seems like, short of finding an old Holton worker from the 70s to talk to directly, this is the best I'm going to get. Seems close enough!