This is what I did:
I left the follower itself alone. I compared the height of the follower hump to the one that was working and found them to be identical. I also noticed that the right-most tab on the mag body was bent up more allowing a higher follower hump over the top edge of the mag. Upon hammering the tab a bit this reduced the follower height and I was able to make the follower profile appear more like the other mag. The result is rounds are no longer popping up out of the receiver, but sometimes the right-most cartridge will get stuck. The other mag does not do this. The left-side tab doesn't seem to have much of an effect on the follower position. I have not touched the rear tabs. Not sure what to try next.
This endeavor brings up an interesting question. If the Brits matched mags to each rifle what was their procedure? Is there a check-list of things to do, or is this all lost to time?