Was a method ever developed for users to determine a lens focal length in order to select the correct/closest rangefinder cam - either for the Speed, Crown Graphic top mounted rangefinders or for the Super Graphic?

I've been working on that problem off and on for a couple of years. You can make a crude nodal slide out of a miter box, a 2x4, and a dull nail.
This set up can get you close but no where near the 1/10 of a mm that cams are spec'd to.

I've talked with "lens people' with the idea of getting an optical bench and offering the service, but most benches are '3 meters long' . Well my wife just doesn see an optical bench as 'an interesting credenza' especially when it blocks the kitchen door. and it would be criminal to put it in my unheated, unlevel, garage with all my wood working dust.
so from my perspective, the answer is, at least at this point........ No.