My Rossis have all been chambered in 45LC. I just read the internet about the 454 version - Everywhere I've ever seen info on the topic, people say the Rossi in 454 will also cycle 45LC (just like the 44Mag version cycles 44Spec, and 357 cycles 38). But then of course, some individual R92 rifles have problems with this. Heck, some individual R92 rifles have problems with cycling the ammunition they are primarily chambered for. It's no mystery though, cartridge length is a particular challenge for most lever gun designs. It is kind of interesting that Big Horn Armory goes out of their way to say that their version in 454 Casull is "unlikely" to cycle 45LC properly.
Since Prophet River has posted to this thread, maybe they can chime in with their opinion.
The poster who posted that he was putting a rail "in" the dovetail wrote a clarification above. I agree that mounting a red dot via the factory d/t holes is a great option.