Ok this is bordering on insanity. I did a Sheldon BB upgrade on a 1973 Supercourse, used the original cups and swapped the spindle to a 173MM MTB spindle to go cotterless with a Stronglight 104 crankset.

Everything is fine with the BB itself, and the drive side chainline is perfect. The left side however could come in a bit more, like 6MM.

Has anyone ever tapered a spindle slightly with a dremel to snug it up? I know using a file would take days, being case hardened steel and all. (Not sure if I want to take a file to the inside of the crank arm (cringe).

This is one of those minutia things that just irk you a little. Could it cause tolerance problems and creaking... probably, if you shaved too much (sigh). Versus time spent endless searching for a spindle that would fit a Stronglight married to a British bike, a strange combo. At least I ditched the Mafac Racers, they squealed like a pig...