Something interesting, maybe, for a few. I removed a factory Hydrovac from a '57 GMC to use on a Chevy when I was a kid. One thing that surprised me was the copper brake lines. I knew it was illegal and that steel should always be used.
Looking through a GMC parts book today I see that folks looking for brake a line for a Hydrovac equipped truck were directed to make the lines from a 25' roll of copper tubing. So I guess that answers that question.
http://www.gmpartswiki.com/getpage?pageid=24167