I am pretty  sure that the underside of the eraser table would have had a thin layer of felt on it.  Thin craft felt, stuck on with contact adhesive (as per the original) or UHU glue should do the trick.  I have never seen an SG1 with '7,6' engraved in that position, but my educated guess is that it is an indicator of the shift pattern, i.e. 7.6mm between upper and lower case characters.  Yes, it is chrome on the linespace lever.  .  A chrome-plated aluminium die-casting.  You could either have it re-plated, or (cheaper option) strip off the chrome altogether, polish it and then apply a coat of clear lacquer

A curious thing has happened: my typing habits have improved for not having the right margin stop.

I've left this machine on my typewriter stand for the last month, using it exclusively, tuning and finessing it as I get to know it better. Because I've still not found or made a suitable replacement for the right margin stop, I left it out entirely (much easier to do the CAD work when it's not in the machine). So, typing without a net (or margin bell), I've had to mind my right margin myself.

And, interestingly, my page layout has improved. The right margin looks much than I produced with typewriters with a functioning margin stop: more consistent line to line and nicely balanced from the right edge compared to the left margin. Since I've no bell, I attend to the line wrapping much more, without distracting myself too much from the writing. In fact, it feels less distracting than being jolted out of the flow by the bell. Maybe it's good to not rely on mechanical conveniences so much...

It almost makes me want to spend a month on one of my blind-writers... almost.


 

Each of the type-slugs are engraved with the 7,65 as well.

I had some time this weekend to do a little 3D modelling and successfully 3D printed a new right margin stop body to replace the crumbling one that came with the machine. 

On the left, the margin stop body from my SG-3 (which I used as reference), and on the right, my 3D printed version in PLA:



Here the two are fully assembled in the same order, with the remains of the original margin stop body on the far right:



Fully assembled and mounted:



I've only written a few pages on it (some with a narrow column), and so far it seems to be working fine, though it's only printed in PLA. I suspect that will hold fine as the right margin doesn't experience heavy loads: it only engages the line lock and triggers the bell hammer. It doesn't actually stop the carriage (the SG-3 works this way too). The left margin stop, however, does get the full force of the carriage return, but that one's metal seems to still be in sturdy shape. I wonder if it was replaced more recently than the right stop.

This was my first attempt at a replacement part for anything, so it pushed my skill and the tolerances of my printer a bit. If I were more patient, I'd probably have iterated on it a bit more so that it worked absolutely perfectly without any cleanup, but instead, I ended up just using files and an x-acto knife until I was satisfied with how it was working. It's a prototype, after all, and because it requires supports, there will always be some cleanup anyway.

I've posted the model on Thingiverse if anyone needs to print their own: Olympia SG-1 / SG-3 replica right margin stop body by robmckaughan - Thingiverse
 

Rob,  is another material option the use of ABS (Plastic) ?.  Do 3d printing folks use ABS ?