Now, since the M&P is a fixed sight revolver, how can an adjustable sight revolver be a pre-M&P?
From the beginning of the Military and Police line most were fixed sight guns but target versions of the guns were offered. The had the front and rear sights shown in your pic.
I would of described the gun this way (without knowing the serial number I go by your 1920s DOB)...38 Hand Ejector Model of 1905, 4th change Target Variation. I would have added that it was part of S&Ws Military and Police line of guns. I believe by then that S&W was calling them the M&P line. I would not have called it a pre-M&P.
I also would have encouraged you to get a copy of the Standard Catalog of Smith and Wesson. Used, good condition copies are available for a small investment. Fun reading and very useful over the years.
If you really want all the details, including where it was shipped to by the factory and when it was shipped a letter from S&W historian Roy Jinks will do that. Also be more accurate than what I'm recalling here.
Sometimes people make mistakes in internet forums. Shocking ain't it!
Nice looking gun by the way.