-
what is the advantage of an especially narrow q factor?
Ask @xavierdisley (http://etheses.bham.ac.uk/5523/) but it's not "especially narrow" which is advantageous, it "self selected" and most people not bound by off the peg cranks will self select something significantly narrower than the 145-150 imposed by normal road cranks, and possibly something even narrower than the 131mm of Campag Pista
If you're shopping for a file for this job, try to find one designed for aluminium. Common files designed for steel will cut aluminium, but they clog fast so you spend more time cleaning your file than actually filing.
That's a feature, not a bug. Campag Pista have the narrowest Q of any current track crank. You can dent your stay or file your crank :-)