I recently came across some eBay auctions which alluded to the fact that the Columbus tubing decal varied slightly through the 70's and thought that might be a good way to help narrow down the year of a bike from that decade if there are no other means. Here's a first go at it:
http://chainedrevolution.com/
Comments, corrections, and suggestions much welcomed.
Cheers,
Tam Pham
Huntington Beach, CA - USA