Obviously a refinished gun imo. But a stellar letter for what it is. A quick look at some of the photos made me think two different engravers in two distinctly different time frames.
It would seem the hammer checkering totally missing. Their is an off chance a close inspection of the hammer might give you a general idea of the date on the refinish.
I would question the "ejector rod housing" observation. I don't have a question that the gun has some wear prior to the refinish as it was certainly buffed heavily prior to the refinish. The ejector rod housings of that era were nicely beveled in a similar fashion as the OP's gun, during the same time frame. I don't think that is holster wear on the ejector rod housing but intentionally done by Colt. It is a 2 minute job to do so. Nice details still intact for the age of the gun. The ejector rod has the correct crescent shaped head and a hole in the cylinder pin head is original. Nice, original touches.
It would seem the hammer checkering totally missing. Their is an off chance a close inspection of the hammer might give you a general idea of the date on the refinish.