Thanks for the replies, fellas! Shame to shorten the arbor just when Uberti was so close to getting it right, but that thought did cross my mind. Incidentally Mike, installing an adjustable wedge bearing is something I usually do now anyway, thanks to you.
One other thing has crossed my mind, and it IS tempting....
I know you don't do this, but I, myself do often lap the barrel assembly against the frame as part of my fit-up. Like you, I fit the spacer so that everything bottoms out with very tight endshake, but I do this with the barrel rotated 45 degrees so that the bottom of the frame doesn't interfere. This usually means that by the time I have my desired endshake, the bottom of the barrel assembly has moved past the end of the frame a few thousandths. I know we've discussed the harmlessness of slightly pie-shaped cylinder gaps before, but I just don't like them. So after fitting the arbor depth, I pull the frame pins and lap the barrel assembly to the frame until it won't lap anymore. If I were doing this for a living, I'd have to charge too much, as that lapping-in does take a while. BUT, I end up with a bottomed-out arbor fit and tight endshake with an even cylinder gap. So... it IS tempting with these very close arbors just to lap these barrel assemblies onto the frame sans spacer until the arbor bottoms out and then dress the rear of the barrel with a facing cutter to achieve my desired endshake. That would save me the trouble of making a spacer, and I'd have more meat on the end of the arbor (more threads in the hole for the adjustable wedge bearing). Still thinking on it....
Regardless, can you tell me again which stainless steel screws you used to make your spacers? I dropped the brass spacer for my Walker in the gravel last week and hopelessly lost it. This was my very first arbor fix project for which I'd used a brass locating pin from a Dillon reloading press, and it was just sitting in there loose. Regardless of how I decide to address these latest revolvers, I'm going to have to replace the spacer on my Walker, and I've decided to make it out of one of those screw heads this time and epoxy it to the bottom of the arbor hole.