Seems like we've solved it! The main thing that threw me off was based on my cadet experience in Camp Argonaut (CFB Gagetown) where we had probably 10-15 of these rifles on the summer ranges.
The cadet use rifles were all Long Branch CNo.7, postwar 1940's production if I remember right, and all had the magazine body stamped with "22" but were fitted with .303 magazine followers. I wonder if that was a result of short supply, or a matter of parts breakages from repeated strip and assemble drills for over decades at the hands of teenage cadets. I do know part of our strip and assemble was to remove the magazine follower and spring every single time, that was bound to take a toll and incur broken springs.

For some reason it had never occurred to me that I may have had a .22 cal follower in a No.4 body, you look at something for decades and it just doesn't click.

Now who wants to sell me a rifle to go with my magazine? LOL.