So, my thinking is that the Dura Ace 7400 that's fitted to my TvT
just now, has just enough fork column thread to connect to the headset. If I look for a C Record Track Headset, being shallower than the Road version, I should be in with a chance of it fitting in place of the Dura Ace one.
If you wanted to keep it all shimano, I recall one 105 version had a really low stack height. I'm not sure of serial no's, but it was a mid 80s one in dark blueish finish. Of course, 105 is a few gruppos lower in pecking order, and you may be aiming for top drawer components