First of all, thanks to all of you who kindly came up with well conceived plans of action. I think you'll appreciate how the successful extraction unfolded this morning. Rather strange, in fact:
Mike brought his fork over. I fitted my dremel tool with a tiny (1/8") "countersink" bit - just to start a well centered hole, for a drill bit to begin the work without wandering.
Then inserted a 1/8" drill bit into the dremel and decided to just drill the hole free-hand (yeah, Mr Over-confidence). As luck (or patience) would have it, I soon got through, and with as straight centered a hole as anyone could ever hope to simply eyeball with a hand held drill.
I was then going to actually try to call around and see if I could locate a store with a small enough extractor, and try that route.
BUT... my impatient friend vetoed that idea and asked if I could instead just drill it out a bit more. He would then just use smaller bolts with nuts & washers fastened on the insides of both of the front the eyelets. Seemed like a very good (i.e. very EASY) solution to me.
So, I escalated to a larger 5/32" bit which I figured might actually be enough to clear a 4mm bolt. I have spare stainless steel nuts bolts and washers, so this seemed like a good size to use and it would keep from enlarging the eyelet hole excessively.
After I was half way through the remains of the stuck 5mm bolt, the drill just punched through. And, on the end of the bit was wound all that was left of the screw itself. 95% of this threaded "shell" of the original screw was still intact at the end of my bit, the tiny portion which was missing from what otherwise would have been a complete cylinder of screw thread for it's entire length, apparently just reduced to dust or left broken into fragments in the eyelet.
Yeah, okay, so maybe dead-eye Bob did not in fact drill an absolutely perfectly centered hole after all... but, mighty close.
Nevertheless, the screw miraculously was taken out, AND the eyelet threads were left intact... and, I DID then clean them out with a correct M5 x .08mm tap before I let my buddy run home to put his bike back together.
I'm still left wondering now whether someone had not previously just tapped the holes either originally, or certainly at least many years ago, with a BCS or SAE thread. And, remember, that frameset is of British origin. If anyone happens to know off hand whether there is in fact a fairly common NON-metric bolt size slightly smaller than a 5mm but with essentially the same threads per inch please do let me know?
Well, this was definitely a very interesting morning. Again, thanks so much to all for all the help and encouragement - I wouldn't have had any ideas on how to proceed otherwise. Gosh, you even made me a HERO, too - Bravo to you guys!
Bob Hanson, Albuquerque, New Mexico, USA