The mounts do appear identical, but one could mount many different scopes on such bases. I doubt the gunmakers who obviously made these up for the Ross M10 intended to be limited to only one scope, unless that was their "house brand". The 'hook & peg' design was used by both Alex Martin & Co. and George Gibbs & Co., before, during and after WWI.
So far I've never seen the Pernox mounted on any other than Germanrifles & Rosses. They are a rare scope, with probably not more than about 1500 made, at the most. Serial numbers that have been seen actually suggest far fewer than that, perhaps a few hundred.
A roof prism as the erector cell is an unnecessary complication presumably done to compete with the Zeiss prismatics from a marketing point of view and perhaps to reduce the number of glass surfaces through which the light must pass. In those pre-coating days, every surface meant a loss of transmitted light. I have a Pernox 3.5x and it is a very bright scope for its day, but not bright enough to justify the cost probably, which is no doubt why they didn't persist and Goerz went on to conventional convex lens designs.
There is no accumulation of dirt, grease etc in the places one would expect it around the scope base, and the screw slots are damaged.
One locating pin appears to be missing and the other looks like it has been in and out a few times.
Can you be certain that the base was originally fitted to this particular rifle?
Has the rifle been refinished recently?
Is there a gunsmith's name?
The checkered trigger is a unique feature.
What does the "C.R.2" refer to? "Charles Ross" perhaps? There was a .280 Scotch Deer Stalker in the UK with a "C.R. to XXX" marked escutcheon plate that may have been a presentation by Sir Charles.
(Rather pointless to proof it at 18 tons in the UK when it had already been proofed to 28 tons in Canada!)
Barrel appears to have been shortened twice: once down to 26"(?) and then perhaps about 3/8" the second time? I say that because 28" was stock and there is almost always a good 1/2" of barrel past the foresight base. Of course it could have been set up that way from the beginning if the customer or smith preferred. After all, the M10 with Pernox in TRRS has a similar 'short' muzzle, so perhaps that was their 'house' style. Might be a clue as to which gunmaker it was.
What is the small circular mark divided into three sections? It looks like "BC4", one character in each section.
Sir Charles obviously owned many rifles, but this may have been a combination that he ordered or at least initiated. The M10 with Pernox scope that E. C. Crossman called "the rifle of my dreams" was provided to him by Sir Charles it is stated in The Ross Rifle Story. If the mounts on the Crossman rifle are identical to these, then that would indicate the rifle must have been in the UK for the fitting of the mounts & scope.
That being the case, I wouldn't be surprised if the C.R. does refer to Charles Ross in some sense, this being the second of who knows how many and for what purpose.
6948 is a very low number for an M10 and early in their production was when Sir Charles was trying to promote the M10 by giving, or perhaps loaning examples to influential writers and figures.
The M10 in The Ross Rifle Story that has these mounts has a 30.5 inch barrel which is unique on a M10. The rifle is described as "Canadian Ordnance and Britishproofed" and serial numbered 8876. One wonders why it would be "Canadian Ordnance" proofed, and when...it might very well have been a sniping setup that Sir Charles tried to interest the authorities in during WWI. The 30.5 inch barrel would reduce flash and help accuracy, despite being rather unwieldy, but then Sir Charles like Sir Sam Hughes, had never been in a front line trench.
Frank Iriam a sniper of the 8th Battalion CEF knew the .280 before the war and tried to get his CO to request some through the "War Office", that came to nothing of course, so eventually Sir Charles was contacted directly and replied that he had two rifles which he would provide, obviously with scopes, but the officer deputed to meet him in London and collect the rifles went out on the town and forgot the appointment. When they asked again Sir Charles had left the UK and that was that.
Other than the Zeiss prismatics a la Lt. Greener, one Voightlander Skopar 5 shown in TRRS, and these Pernox scopes, there were probably very few scoped M10s or Scotch Deer Stalkers pre-WWI. Almost all the scopes that are seen on them now are either surplussed WWI sniper scopes fitted in the 20s or 30s, or later types like the Lyman Alaskan and Zeiss Zeilklein.
Who knows, maybe yours is one of the rifles the 8th Battalion were supposed to get!