HELP NEEDED: 1950 Model 16H Plunger Frame

Hello, all.

To quote the late, great Prime Minister himself, I appear to have on my hands a riddle, wrapped in a mystery, inside an enigma.  If not that, it may just be an inherited kludge.  

My Model 16H has been identified by the NOC as a 1950 year model originally sold new in what is today known as Pakistan.  I have been working over the last several months to get the old girl on the road, and having gone through the engine, the primary drive, and the gearbox, I am now turning my attention to the rear hub and suspension.

I had not noticed this until now, but my rear plunger arrangement appears to be unlike anything else I’ve seen on a Norton.  Instead of having both upper and lower springs, my machine is fitted only with upper springs.  This is to say that I have an accommodation for compression, but none for rebound.  Moreover, when the upper spring is fitted, there is very little space available for a lower spring.  I purchased new upper and lower spring covers (sliders), and to be able to fit them into the available space, both springs, if fitted, would have to be fully compressed.  Such an arrangement would render the plunger suspension useless.

The further I investigated the matter, more and more differences became apparent.  Instead of having a lower slider fitted, mine had a rubber boot that was dried out and nearly perished.  Furthermore, the plugs I had bought to fit into the top of the slider tube were much smaller than the ID of the tube.  I also noted that the tube did not have a spiral relief machines into it, but instead was smooth with a series of holes drill right through at the extreme ends.

The distance from the top face of the lower perch to the bottom face of the top perch is 226 mm.  The OD of the slider tube is approximately 0.788” while the ID is approximately 0.547”.  For reference, the OD of the plug intended to fit into the top of the tube is 0.375” (3/8”).  The spring as fitted measured 145mm in length x 44mm in diameter (5 11/16” x 1 11/16”).  Please refer to the attached pictures.

So, what do I have on my hands?  Has someone possibly attempted to fit a plunger rear from another manufacturer?  If so, any ideas what these bits might be from?

Thanks in advance!

-Robert