Great project Joe. I've got a couple of modern reprint magazines of some planes from the 30's with a few blueprints, but with 5000+ they are almost sure to be dulicates.
Off the topic, but it would be neat to scan those blueprints into a program like
http://www.raster-vector.com/, find some way to automate the 3D modeling process, and then fly them in an open source flight sim like
http://www.x-plane.com/.