Wrong shock absorbers

Did the earlier bikes have more room ?.

STD wideline and I think Slim line and Commando all have 2-1/4 (or a bit less) (58mm)

I don't know if it's lens distortion on the photo but they look a bit like jampots from AJS and Matchless models from around 1956.

As Alan said standard fit to the wideline bikes 

... jampots as well but those have a clevis lower mounting.

You don't mention which model year you have, but pre-1956 models had Armstrong rear shocks, which were a little larger in diameter than the later Girlings. They tended to have a chrome lower spring cover with a knurled ring, which yours do not have; but not all did.

Does it matter all that much? If they are wrong, they are wrong. Replacements are cheap enough, and work well in my experience. As such, s/h ones won't have much value, even if you do find what they were designed to fit.

Working on my 63 SS i find the orriginal (very rusty) shocks still have all the rebound damping I can use . Good old brit engineering .  Jap stuff of the day had useless damping when new .

Richard. Living in SA does put a different complexion on it! All the more reason why a previous owner fitted whatever he could get hold of, perhaps?

I have just measured a set of Armstrongs I have; not off a Norton; and the top shrouds are 2 1/2" diameter, so 1/4" shy of yours, which makes all the difference, obviously.

My guess is they are not off a British bike, possible off a European manufacturer, so you could have your work cut out identifying them.

Good luck!