Have to love the historical guns, shame about the non-factory re-blue.

The dishing around the S/N on the butt is a dead giveaway that someone else did it, also if I see right the hammer/trigger are polished?

I may have missed it, coffee not being in brain yet goobers my reading comprehension, but have you taken off the stocks to check for a stamp on the frame? Something like X.XX?

The S&W Historical Foundation has records over a particular period (I'm not sure what is digitized yet), and there is a possibility of finding records regarding what the service department did to the gun if it happened over the period they have recorded.

I just got a lovely package of information on a modified police gun of mine. Also it's an example of S&W factory re-bluing. I think you will see the difference between your cool gun and this one:

Half Target M&P, Update: Another Police Gun!

I cannot stress how incredibly cool the Historical Foundation is, everyone should be a member and support what they do.