Have you ever done something that turned out to be REALLY DUMB?
Some time ago I acquired a nice little 2X3 Crown Graphic and had great fun using it. One day the shutter quit operating as it should so I took it to my friendly camera repair guy.
He examined it and found some broken gear teeth etc.and said the shutter was old enough that more problems were apt to present themselves down the road. Here's the dumb part: I had a 90mm lens in the same shutter sooooo I had him make one good shutter from the two and install the 90 in place of the original 101 mm lens,not thinking all the focus adjustments would be wrong!( just wanting a little wider angle lens as I was shooting scenic's at the time).I've tried to change the distance marks on the bed and am having some trouble getting sharp images so far. Have tried focusing at measured distances from a subject on the ground glass using a magnifier and still having some problems. Why I didn't leave well enough alone I'll never know LOL!
I guess you will just have to use the ground glass to focus for a while. The current focusing scale will not be right for the shorter lens, but you may be able to make a new one that will work. The movable part is what needs to be changed. I'd recommend a chunk of adhesive label on a piece of aluminum. Not very sturdy, but easy to do and easy to change. Do the math, make some pencil marks, then check it against the ground glass before making thing permanent. Keep the current scale, just in case. Even if you have a decent scale, the rangefinder will be off. The difference between 90 and 101 mm is enough so that you will need a different cam. Scan the web, you may find one or you may be able to make one. Unfortunately, attaching and adjusting the cam is a very difficult and frustrating process (I've done it - ouch). Maybe the best solution is to look for a 101 mm lens and shutter. They're pretty common on the used market. You can also find lens boards, so you will have two lenses for your camera.
I have never seen a 2x3 Graphic with a top rangefinder. The Kalart rangefinders do not have cams. The Hugo Meyer rangefinder also has no cam. I may be wrong, but I have never seen a baby Graphic with a Graphic (top) rangefinder.