Here's the story of Area 51 Nat Geo did a few years ago. I thought it was a pretty good documentary:

part 1 of 4: http://www.youtube.com/watch?v=jcJzDqxqmEc

It talks extensively about the A-12 project. I thought the most interesting part was how they shipped square parts in round boxes and round parts in square boxes to conceal what was inside.

Different time back then for sure.