Yes, guilty as charged for buying this one. I spent quite a bit of time asking myself these same questions. Given the fact that this serial number could be a 1917 Army; .455 2nd HE; or a 1917 Transition based off of serial # alone it obviously needs some more research and work, to which I thank you all for commenting already. I have already learned a few things to look for from these posts I did not know. Much appreciated and I will keep you all informed.
In my opinion the gun is a early post-war transition build in 1946 or it is a late .455 HE 2nd.
Pros/Cons for being a .455 2nd:
Pros: Serial Number range; Pre-War location and font/stlye of serial number; Barrel Length; if it is in fact an original special order .45 Colt then the barrel would only be marked "Smith & Wesson" on the left side with no caliber designated; pre-war trigger/hammer; lack of stamps/markings indicates a commercial variation; pre-war ejector
Cons: Post-War style large S&W on side-plate; Serial number on cylinder appears to be post-war font, absence of .455 mark on barrel, location of "Smith & Wesson" on barrel is centered on gun and in a different location than known commercial overrun .455s (further supports .45 Colt special order or a barrel swap); trigger pin smoothed (implying post 1920s production or done in refinish), most of these factors could have happened during 1946 refinish.
Commercial .455 Overrun
.455 British Svc Revolver Research Thread
Late special order factory .45 Colt (.455 2nd HE)
2nd Model HE, .45 Colt
Pros/Cons as a transition Post-War 1917:
Pros: Perhaps this was a prewar frame from a left-over second model as the serial number was a late .455 series and perhaps assembled in 1946 which coincidentally is in the appropriate serial number range of N-frames (38/44s) etc made in 1946; refinish date ties gun to 1946; pre-war and post-war indications, pre-war frame but with post-war style serial number on cylinder and post-war style S&W on side-plate; I assume the frame was serial numbered with the barrel during initial assembly and the cylinder and final roll-marks are applied during subsequent assembly...corroborated by "10,868 frames were numbered in the 1930s but not completely assembled until after WWII" "991 new Model 1917s were produced between 14 May 1946 and 25 July 1947...these continued in the prewar serial number series" (Jinks); "it is likely that they have a mixture of pre and post war characteristics. Probably they do not have the "S" hammer block, and therefore would not have S-prefixed serial numbers" (source The Fifty Years of the S&W .45 US Service Model of 1917). This is all conjecture... thought it could be a left over N-frame assembled in 1946 for a special order basically, and that would most align with a .45 1917 Commercial was my line of thinking.
Cons: Barrel Length; Not marked S&W DA 45 but Smith & Wesson;
Other important information, my main question for the seller was whether or not they chambered .45 acp and .45 Colt. They stated that .45 acp fell directly through and .45 Colt seated well with both a opened/closed cylinder. It could have been a .45 acp originally but the detailed photo of cylinder rear and ejector star do not look converted from .45 acp to .45 Colt.
King or S&W could have simply replaced barrel and cylinder. May never know.
The Letter not shown but quoted by seller, was puzzling. I asked the seller and they admitted that the letter was rather dated 1990s and the current configuration of the gun did not obviously match. So instead of causing more confusion they cautioned and chose not to include. The letter read as if the request and answer were for a 1917 US Army and stated a 5.5" barrel. So I think the letter request back in the 90s described the gun as a 1917 and therefore Roy saw the serial number and lettered it as a converted Army 1917. I think the existing letter is in error, but that was my gamble. This gun needs to be re-researched to confirm or deny the other two possible guns with the same serial number is my thought.
I have always wanted a King Super Target, I collect .45 Colts and Custom Target Stocks, this checks all of the boxes. I have only been serious at this for a few years but there is perhaps a handful of .45 King Super Targets out there, I've seen two and the other was a .45 Acp 1917 Army. If this is an original .45 Colt then heck yeah, but even a factory converted .45 Colt pretty darn cool. Worst case it's a .45 acp that maybe chambers a .45 Colt. I was taught to buy it when you see it!
UPDATE
.455 H.E. Second Model serial 73193 was shipped in July 1916.
So it was a .455 H.E. Second Model. It is late in the serial range, currently a .45 COLT, and no proof of being a .455, my guess/hope is it was one of the .45 Colts shipped to the Canadian Government that has been King converted and factory refinished in 1946. I don't think there are records by serial number of those .45 Colts shipped to Canada so we only have the gun to judge?