Sounds like a plan, but there are other approaches. Your plan as stated has two problems: a bellows by itself is pretty floppy and "a contemporary mounting ring" doesn't focus.
Originally Posted by gnolanphotography
What I do, more for assessing the lenses' central sharpness than for serious picture taking, is attach the salvaged lens to a focusing bellows for an SLR. I shoot Nikons, have three bellows for 'em. Nikon PB-4, a Zenit in M-39 with an adapter to Nikon at the rear, and a Minolta Compact Bellows with adapter to Nikon at the rear. I use the first two with "salvage" lenses, prefer the Zenit because it is lighter. The Minolta Compact Bellows is a marvel but I use it mainly with macro lenses, e.g., Zeiss Luminars; it is too short to focus most of the lenses I've, um, salvaged.
Although I've salvaged a number of lenses from ancient folders, I don't limit myself to just these lenses. I've shot a variety of lenses intended for 4x5 and larger hung on bellows in front of a Nikon.
I mention Nikon only because that's what I use. What I've done with my Nikons can be done with most, probably all, other 35 mm SLRs.