timming question

[fdbdw]

71 c10 350/points
I currently use a timing light and am set a 8 btdc, i was told by a guy at the parts store that because I live at high altitude that it is best to set timming with a vaccum guage. He said to connect to the vaccum port on the back of the intake manifold and adjust the timming until you get the highest vaccum reading possible and leave it there. He swears by this being the most accurtate way to set timming. Has anybody else use this method and does anyone have an oppinion on vac vs. timming light.