Velobase.com

I've recently spent a great deal of time on www.velobase.com

"your vintage cycling database" or in their own words:

"The goal of VeloBase.com is to provide a comprehensive database of vintage cycling knowledge for reference during everything from restorations to general maintenance to researching the cycling history through the equipment of the time. All of the content on the site was added by its members, truly making it the cycling community's database."

Off course there are others like Classic Rendezvous, Wooljersey (temporarily down) and Bulgier.net but I've found Velobase the easiest to use so far.

The catalog of parts is pretty comprehensive and it will allow you to really start nerding out about the correct model / type / year of your vintage bike build.

Enjoy!