C96 Lock frame Break

I found a C96 Red 9 police rework at a show and after deciding it was authentic, numbers matching and has great blue, failed to notice the frame lock was broken at the base of the ejector. The piece is missing so I'm looking at either replacing the frame, or cutting two frames to weld one together. I don't want to take a loss on this one so I'd like to figure out some way to make it work. Like most other old guns, parts aren't always interchangeable, but what are my best odds of a successful repair?
The SN is in the 7xxx range, with a 1920 barrel date.
At the time of writing this post, I found 3 stripped frames for sale, 815513, 650528, and 691715. Would any of these frames be likely to fit? The 65 and 69 frame visually look the closest.
If a fitting a lock frame is unlikely, how plausible is cutting and welding?

Somehow fit a lock frame somewhat successfully, except for the lower sear, sounds like the trigger is falling off the sear before it pushes the hammer sear up. It appears to have been filed more recently than 1920, so I might try a replacement or new sear. Would a steel reinforced epoxy be strong enough to build out either the sear or the trigger if necessary? Are there any sources for sear parts?

Edit: It only does this if I drop the hammer after opening the bolt. If I install the lock with the hammer off the sear, subsequently cock the hammer, the trigger drops the hammer every time. It works until I pull back the bolt, and then the trigger does not function. Am I looking at the wrong issue?

Edit 2: On pulling the bolt back the barrel moves back as well, to drop the lug. As the barrel moves back, the lock assembly moves back a fraction of an inch, and the trigger misses the sear. If I press the lock forward the trigger works. The only part I'm aware stops rearward motion of the lock is the lock release.

Reference pistol lock also moves back slightly. Good sear from a reference pistol does not work. Lock stop from reference pistol does not properly fit, hammer will not drop to firing pin, but trigger works because lock cannot move back. Might be looking at the trigger portion of the sear as well. The reference trigger sear is significantly deeper and sharper.

Those are all hand fitted I think, not likely going to find drop in parts.

I think I've isolated it to the spur on the plunger rocker. Compared to the reference pistol, and an understanding how the trigger sear works, if the plunger is too long, the sear can't rest on its designed rests, bringing it too far away for a worn sear to lift. If I file down the plunger spur, and replace the lock stop to reduce play, I should end up with a functioning C96, if out of spec.