Denny - the thread for the various size inverted flare should be a tubing thread, and a tap should be available (at least they were when we ground our tooling for flares years ago). If not locally, try J & L Industrial Supply.
Start with an end mill the proper size for the thread, and grind out the center of the cutting end to cut the flare.
Now grind out the center of the appropriate taps (you will need a plug tap and a bottom tap) so they do not disturb the flare.
We had to fabricate these tools in order to do "number maching" factory multiple carb restorations. Many of the fittings on the factory multiple carb set-ups are absolutely unique.
Sometimes one simply has to look "outside the box" to repair something.
Anything that has been made by man CAN be made again by man. The important criteria often is the cost.
Jon.
