I would avoid using shellac, which is alcohol soluble, which means it may become contaminated with water.
Interesting website. At first I thought it probably was just another audiophool page. I looked at their transformer catalogue page, and the prices look realistic. I haven't surfed the whole website, but what I have seen so far suggests they may actually know what they are talking about, not playing with smoke, mirrors and snake oil. Audiophools have given anyone who who appears to be involved with audio technology a bad reputation. I'll check it out some more when I get time.
http://home.att.net/~chimeraone/vintagetrans.html