Jim
You raise good points. A friend of mine (fellow S&W collector) personally examined one of the Canadian 45 colts. One of the tell tale ways to counter your assumption of a converted .455 is to see how the gun was made in 45 colt. Factory examples were made in the same way as the 44 special, whereas the large thick case rim issue would have been solved by positioning the cylinder appropriately, so there would be clearance. This would have necessitated most likely a shorter forcing cone, IMO, or perhaps a shorter cylinder. Logistically, the .455 cylinders were probably used, but were reamed and placed in a position where clearance was achieved. Countersinking would not have been done by the factory to achieve this. Aside from all of that, there is little likelihood that between both reaming and countersinking being needed that even a great gunsmith could fool everyone. There would be a difference between the two (factory 45 colt vs conversion) as its unlikely any gunsmith would have converted any .455 in a way that S&W made original 45 colt guns. If they were already tooled up to make .455s, 45 colt would not have been very difficult IMO to make simultaneously.
IMO the Canadian logistics issue(s) in this regard would be minor, since it was only 724 revolvers, when they were getting tens of thousands of .455s. I doubt very much government 45 colt revolvers would have required tons of ammo. Also, in a sense, it makes more sense for the Canadians to purchase 45 Colt guns (assuming there was a need) since S&W got the contract for the .455s over Colt. From a logistic parts perspective, everything would interchange except the cylinder. Everything else would be the same. So in other words, since there would be so many .455 guns and parts, it does make more sense to order 45 Colts from S&W over Colt. As for the ammo, they would have already had some 45 colt on hand due to the New Service contract.
As for the 45 Colt guns being part of the MKII series or not, I was told their SN falls in line with MKII series SN range, and they may have their own range, although I never came across this info.
The "724 guns for Canada in .45 Colt" sounds a bit like one of those stories used to explain why the gun being sold at a high price is not one of the more common .455 guns converted to .45 Colt later on, but is one of the "real, genuine, golly gumdrops special order revolvers for the RCMP and worth $_____ but just for you, I'll let it go for $______" (fill in blanks). (And of course, ignore that dent on the barrel where the second "5" used to be.)
I think the more likely scenario, since it says precisely "724" is that Roy Jinks himself found the actual shipping ledgers with these revolvers and accompanying serial numbers, and he passed on what he discovered to the S&W Collectors association, and then it later was mentioned in the SCSW 3rd. He is of course able to examine the records, and when anomalies or interesting pieces are found, the word gets out. I would give more credit to your theory if there was a vague amount given (rather than an exact number) such as "some known to be in 45 colt" or "a small number shipped in 45 colt to Canadian government."
I will attempt to get a photo from the one collector (and perhaps one other one) who I was told has one. I could then post it here. I agree it will be interesting to see what it says. It is possible that the 45 colt contract guns were different from the .455s perhaps in that they were made first, or that they lacked the lanyard, etc. I never asked, but its possible that they were actually triple locks rather than 2nd models. There was some overlap of SN btw. IIRC triple locks are 1 to 15000 whereas .455 Second models start at approx 5k. There were also triple locks converted to .455 early on.