Thanks for your ideas/ suggestions, Jack.

But I think I'll leave the displacer thoughts, until this present section's sorted........

Finished roughing, at .005" per pass......

I'm going to face off the 6BA threads, down to below the level of the part thread.....

I'll then reduce the dia of the o/d by .1" per side, right through to the neck.
Then counterbore the new piece, to replace the o/d, and machine a larger flange.....

The original flange is a bit small. Doesn't seal well on the 1/16" cover plate.
Making new 3mm plate with recess for flange, to replace......

Unless anyone else has a better idea?

David D