Well here is the results after making the knob in my lathe.
I used polyethelen and high temp silver solder. However, I dont think the bcg is getting hot enough to let the solder flow. I guess I need to try oxy acet or arc weld it. The other option is to tap the hole, make another threaded knob, and locktite it. I could tell things wernt working right since the solder stayed in this big bubble and did not flow at all. Copper is much easier.
The other concern I have, and is why I tested this on this bcg when I can easily by another and not my saiga, is the heat on the metal. I am wondering if this romanian metal will weaken from the heating to solder it.
The top cover was easy to do. I cliped it with HVAC heat metal shears and evened it out with the grinder.