I'm looking to get a Crown Graphic which has a top rangefinder. From what I've read here (on graflex.org), the top ones may be a little easier to use, if it in good condition, but are overall harder to work on and require custom cams if using a lens other than the one that came with the camera (in the case of the one I'm looking at a Schnieder Xenar 135mm/f4.7).

But I also read one can use a secondary distance scale on the focusing rails to compensate. This was in the Kalart rangefinder adjustment article (here). Which of course is not the same as the top RF. However, the principle should be the same, correct? Copy/pasting the paragraph specifically:

Leave the camera set up as is, but add a second distance scale to the focusing rail. View through the rangefinder, and read the distance on the existing scale, which corresponds to the rangefinder setting. Then, refocus until the same distance is read off on the second scale.

I realize this is a stupid question As long as the RF is accurate to that distance scale, regardless of which type of RF it is, the above trick should work correct? All I have to do is make a distance scale for the lens I want?

Or I suppose another way to look at it is it's like using an uncoupled RF where I'd match the distance read by the RF, focus using the groundglass for the same subject, and then note the position of the lens.

Right?

Close but not quite a cigar. You'll need a distance scale for lens B and also a pair of bed stops.

You could mark the bed rails to indicate where the standard should be when lens B is focused to infinity, but without stops you'll have difficulty making the standard square on the bed.