So if the screw heads just twist off, I can still drill out the screws? I have a machine shop, but this is very delicate compared to what I usually work with.
Sure.
Here is one way - drill out the threaded end, using increasingly larger drills until the hole almost reaches the edges. Drill only as deep as the engagement length. Then use a punch, and drift out the shank of the screw. The remains will be left in the threaded hole. Pick out these remains.
If necessary, a needle file can be used to cut a V notch through to the very edge; eases collapsing the little ring of threads.
Work carefully, and in all probability the threads in the frame will be intact, and it will not be necessary to rethread to a larger size. Might be necessary to run a tap of the correct original size through, just to clean things up.
Much easier to deal with through holes than blind ones. Just work slowly and carefully, thinking about what you are doing.


















































