I have an old Peugeot frame which I want to build up into a fixed gear. It came with a SWISS bottom bracket in good condition, but with a 126mm spindle. From reading around on sheldon brown's site and bike forums, it seems likely that chainline issues will surface with such a long spindle. I've never built up a bike before so I'm not sure exactly what this will entail (although I'm excited to find out ), and I also read that chainline issues tend to be something you can't over-anticipate, that they tend to be unique for individual set ups, and that you just have to try it out and see how things turns out.
Assuming this spindle is too long for a fixed gear, it seems like people have a hard time finding swiss-threaded bottom brackets, and so I might be better off just trying to replace the spindle? When I talked to someone at the LBS about this, she said that the center part of the spindle is the important measurement to match up for BB/spindle compatibility. Is this true? Are there other considerations I need to pay attention to as well? Has anyone ever swapped out a spindle with a different sized one?