Well, today has been as frustrating as it has been an education.
I spoke to my preferred mechanic and although he initially thought he had a 112mm spindle, in the end I had to settle for a 113mm threadless cartridge.
Threadless, because I was told by another LBS (since gone out of business) that I had an English 68mm bottom bracket shell but the drive side had an Italian thread (presumably recut after being stripped).
I took the BB home but realised that I didn't have anything to get the drive side cup out: 8-sided and 36mm across.
Back to the mech. who whipped it out and put the cartridge BB in, but it wouldn't do up because it's a 70mm shell! In other words I have a "normal", Italian BB and not the Anglo-Italian Franken-bracket I had been told I had...
Given the choice I'd stick with the loose bearing type, as all I actually need is a 111mm spindle but they aren't readily available. So I have a choice of a Campag Veloce
or Tifosi carbon shell
: any comments before I take the plunge?