Cute Kids Joe, and I see that you already have a favorite. 🙂 You borrowed the chrome ring from the rf window of the III and put it on the IV sb. That is something that I would have done too.
I have a III that my brother traded me for a Pentax ME slr I had. He bought the III when he was in the navy during the 50's, shot a bit with it then put it away for 50 years. When I got it the curtains were pretty much rotted out and it was in much need of a CLA. I pulled it apart and replaced the first curtain, patched the second curtain, cleaned and lubed what I thought were the right places and put it back together. It works fine, but it also seems to have a less bright view through the rangefinder than any of several other Canon bottom loaders I have.
My III has a rangefinder patch that is more of a light grey tint, rather than the yellowish tint of the other slightly newer ones. I think they made a change to the finder optics somewhere in the early 50's.
Enjoy the new Kids!!
Paul C.