Just to clarify a little. My main concers for the .45 Colt are not rim diameters. If you look at an authentic, un-retouched .45 Colt case, there isn't enough "rim" to spit at.
THE problem is cylinder wall thickness. When the originals were converted, there wasn't much wall left when cut to .44 Colt. A .45 chamber would result in a chamber wall that is just too thin. In fact, many original conversions in .44 Colt have spit out the little price of metal left in the bolt slots.
Today, quite a few NEW Uberti Open Top guns have come into the shop with the same malady. After a few rounds, they spit out the little bit of metal in the bottom of the bolt slots. Understand though, the guns still worked just fine. I just don't personally feel any reproduction or conversion with cylinders of that size is truly safe chambered in .45 Colt. Push the envelope just a little bit and you have some assembly required.
I like em a lot, however chambered in .44 Spl and shot with .44 Russian cases.
Coffinmaker