I think I've been here before, but I can't remember the solution or explanation.

Quick story is the Chorus cranks I would like to use with an 8S Chorus setup sits too close to the chain stay.

back story. I am setting up a nice maybe late 80s Bianchi. well actually no, it's not so nice. it has great bones but is in pretty grim condition, cosmetically at least. But before I commit to an expensive restoration and paint job i thought I would set this back up and ride it, to see how it feels, to see if it's my size (the frame construction is pretty weird, with these headtube and seattube extensions it's hard to figure out what size it actually is) and to see if there is Love between us.

It came to me as a 10S Campagnolo Record set up. but since it appears to have been left out in the elements for a couple of years, the brifters were seized. So I stripped it and started over.

I left the bottom bracket installed though (because I suspect it might be French thread and I don't want to mess with that, or try to replace it.) It seems smooth.

But 2 of the three sets of similar era Campy cranks touch the chainstay on the Drive side. A Mirage set seems to fit and I will just use that for the testing period.

but what's the deal? BB axle length?
why would some cranksets sit too far in and 1X fit OK? when all seem about the same vintage.