There was a question/answer in the tech section of the November issue of Car Craft regarding vacuum brakes. I thought the comments regarding the master cylinder, boosters, and vacuum levels were interesting altho I am a bit confused on some of the vacuum levels versus booster size...either I am reading challenged, or there may be a typo...
Anyway, I scanned the article:
http://www.vortexbuicks-etc.com/vacuum_brakes.htm