The Canadians bought scopes in December 1914, before anyone else except the Central Powers. The 8th Battalion CEF sent in a request to the W.O. for permission to buy scopes in early 1915 . Eventually word came back that the W.O. had no nomenclature or allocation for telescopic sights so permission could not be granted (or denied presumably!). The same with the .280 Ross: a request was sent in for permission to purchase them and eventually an officer turned up to ask some questions about it, but nothing ever happened.
As you know, some 500 W&S scopes were fitted to Ross MkIIIs and about 180 issued in France, as well as various "Long Lees" and SMLEs with different models of telescopic and Galilean sights issued through British channels. It is most likely the the Canadian issue Winchester scopes were purchased directly, either by the units in France or by the Canadian Department of Militia & Defense. I don't think we know which for certain, quite possibly both. Winchester wouldn't have cared who paid as long as the money was in their account and the Canadians didn't worry about paper trails as much as some others. AFAIK, none have been seen with British inspection marks that do not have SMLE serial numbers engraved on the tubes.
The Winchester scopes were not serial numbered from the factory and AFAWK were not serial numbered to the Ross rifles. There was no reason to do so really as the scopes were pretty much interchangeable insofar as the bases were concerned.
I conclude that the barrels were cut back because they interfered with the field of view of the A5 scope. That's just my personal view and I haven't seen it asserted anywhere else. Otherwise, the front sight base could have just been knocked off and that would have been that. Cutting and crowning the barrel was a lot more work and there must have been a reason, other than making the rifle a couple of inches shorter for handling reasons.
The forends were cut back for all the usual reasons: weight, ease of handling and concealment etc. Somewhere I read that the 3rd Can. Div. did not allow stocks to be cut back, but I can't be sure it was the 3rd without checking.
AFAWK, cases were supplied with the scopes, at least some times; Iriam refers to this and in some photos of scout/snipers case straps can be seen. Later in the war, when it may have become known that snipers were loath to remove the scopes from their rifles, the lack of need for cases MIGHT have led to scopes being ordered without them. Just a guess on my part though.
Have you read Frank Iriam's memoir?
Edit: I see there is a quite a bit more detail about this in "Without Warning" so you'd better get a copy if you want the fuller story.