Agree, sounds like a rechambered .455 TL. I have one of those, S/N 358, but the barrel was not remarked for the longer cartridge.
There were only about 5000 .455 TLs made before the company switched to the second model, which has no ejector rod shroud; they made another 70-80 thousand of those. (Forgive the round numbers, I'm just too lazy to look up the actual figures at the moment.)
I dimly recall that the true .45 LC TLs had five-digit serial numbers. If yours has only four, that's yet another indicator that it is a converted .455.