Thanks Hammer It and Kamerer.
The only other information that I have is that someone posted on another forum that it was circa 1927, a M&P, but never revealed his source.
My only resource book is The Official Gun Digest Book of Guns and Prices 2007and it appears that it's called a "Hand Ejector Model of 1905, 4th change", with that serial number. But I am not sure of this source at all, but it would be consistent with the other poster because book says this was the largest run, and was from 1915 to 1942, with serial numbers from 241704 to 1000000. Of course, the date of manufacture for 540### is not indicated. And I might have the wrong model gun.
Anyway, I just placed an order with Amazon for the S&W Catalogue by Supica, etc. I don't know if it will help but I want the book anyway.
Any additional or other input would be appreciated.