Congrats on your purchase of a Number 4 Mk I* service rifle made by Canadian Arsenals (Toronto) in 1950. Too bad the bayonet lugs have been removed which hurts the value significantly. Your 1st pic demonstarates the date of manufacture (1950)of the barrel, the Dominion of Canada Proof mark placed on all Canadian made service rifles prior to 1957 (est),
including the .303 Ross, and the inspector's ID number who passed that rifle for service. Various parts may have the C broad arrow (Canadian ownership), LB (short for Long Branch factory), CA (for Canadian Arsenals (Long Branch after 1946, or even
others indicating Savage (U.S.) or misc. letters indicating British origin.. Brit and Savage parts sometimes replaced Canadian parts over the years because you never know where it has been. My guess only domestic use as there are no proof marks or import marks visable indicating foreign use. Your rifle is capable of very accurate shooting regardless of how many grooves. My 1958 new barrel is 6 grooved and lug marked but no DCP. Now you can look for a WW2 made rifle as your bolt is 1944
as mentioned. As with all mismatched rifles have the head space checked before shooting. Enjoy. John T.