Very nice rifle Kari, very similar markings belonging to the 2000 DP conversions.
You are correct on the M192 code being Parker Hale's WWII identification number. Many lend lease .22's were marked with M192 and a post war date in order to tidy up the paperwork, for some reason yours was included. I have also enclosed a better, but poor, pic of the PH1941 butt stamp on my rifle.
Upon examination of my Cooey sight on my Canadian .22 Short Mk IV*, I too have the broad arrow military stores acceptance mark, but mine is not as nice as yours. (GOOD CALL, never noticed it until now!!)
This mark I feel was just meant to signify government ownership/produced for government contract, rather than Britishownership as the bases were most likely manufactured by separate Canadian contractor and the sights by Cooey. Not to say your rifle is not strictly British issue, as this cannot be proven either way due to the lack of other ownership marks on the rifle itself. Sight that are not broad arrow marked could be simple Ross rifle removals
This is part of the fun/pain of collecting, you never know....
I have yet to come across a complete Aux. rear sight set up. I did have a graduated rear volley site like yours until I gave it up to another collector that had to have it. I know of a couple complete sets in Canada, but both collectors are willing to wait for their estate sales to part with them!
Thanks for sharing, keep on collecting! Pic's of your other rifle would be great.