Originally Posted by DannoXYZ
You can also easily drill a hole in the BB and tap it to hold the modern plastic cable-guides. Much cleaner looking and won't damage your paint like the clamp-on guides.
This is not going to work in many cases. A lot of these older bikes routed (via the clamp-on guides) the RD shifter cable over the top of the BB tube to a brazed on cable guide mounted on the top of the chain stay.
Most modern chain stays have that rear cable guide brazed on the bottom of the chain stay and expects the RD cable to come from the bottom of the BB tube.
You can't just run the RD cable from the bottom of the BB tube (from a modern plastic cable guide) to a chainstay cable guide that's mounted on the top of the chainstay. It won't work.
The first thing you need to do is see whether the chainstay cable guide is brazed on the top or the bottom of the chainstay. If it's on top, then you need to use the old style cable guides that clamp on to the down tube, like the SunTour or Campy shown above. There is also a Shimano clamp-on that is similar:
http://www.thethirdhand.com/index.cg...id=30093644929