Square tapered BB spindle question

oddsock btw, in case roberto's dura ace 7610 bottom bracket somehow reappears on
the market, does anyone here know if it would have a JIS or ISO taper -
I was hoping it might fit some sugino 75s I have waiting to be fitted (on the
face of it the axle length is right).

Sadly not. Dura-ace is JIS - as is pretty much everything except for Campagnolo and the Sugino 75s. Although all other Suginos are JIS, for some reason, 75s are ISO

Bearing that in mind, a Campy bottom bracket would work for you, or preferably the Sugino 75 model or Phil Wood's ISO taper. The good thing about Phil BBs is that the cups can be replaced very cheaply, so you could move it from frame to frame relatively easily, rather than losing the (not inconsiderable) investment if you decide to get a new frame one day.