This photo is very helpful, as of a little bit ago, I used a point light from my cell phone to look directly down the back tube, only to see discover that, what a multi-LED Lume Panel did no reveal to my eyes, the single point made clear.
I DO have a glass element in the same position of your lens (or group?) and seem to only be missing the long cocking lever to the shutter and the back mounting plate.
I do have a parts plate & screws from another lens I can use, as they appear to be universal and a brass or mild steel flat rod is a simple enough thing to make, if I have the correct dimensions, which I hope some will share.
If anyone else has info/tips/schematics to share or inexpensive parts, I will welcome one or both greatly.
Cheers to all