If you're potentially interested in a dual format 6x6 and 645, the Mamiya Six folder has the 6x4.5 mask leaves captive -- can't be lost without tearing stuff up. Already on the suggestion list, IIRC.
Mamiya Six family model list The late 1940s and the 1950s saw most Japanese camera makers offering cookie-cutter 120 klapp cameras, most named Six or Semi in one way or another. Some makers survived a further decade or two, a few have reached the next century, while most just faded away. These...
The one I have has amber windows. Hard to see the numbers on black-print-on-white backing paper without direct strong light in the window, though -- with the pressure plate and film plane focusing, it's a lot further from window to backing than with most red window cameras. Really, that's my only significant complaint with my Six.
OK, I know, but just in case- Fujica Super-6. Great lens with unit helical focusing, not front element focusing. Auto frame spacing. Simple but accurate coupled rangefinder.
I've had a co9uple of Baby Bessas and Bessa, 6x4.5 and 6x6, and found the Skopar to be an very good lens.
Simple rotating mirror under the top shroud driven by a lever from the helical on the lens standard. Focus itself is a single helical b- unit focusing? I am drawing a blank on the term- not a front element focusing.