I'd buy that one unless it was saddled with a delusional price. A four inch target M&P from before WWI? Sure. I'd like to know that the serial numbers matched on all parts because that could be a four inch barrel that was modified with a pinned target sight and attached to a frame that originally sported a longer barrel. Can you share the serial number? I'm guessing between 100000 and 200000 unless it's put together from pieces.
Don't believe the '20s era stocks.
At $450 or less I'd buy. At $1000 or more I'd walk. In between I'd haggle. Since it is a charming oddity, the presence or absence of a finish doesn't bother me.