Initial Timming?

My question is about setting your timming with a vacuum gauge. I've heard that you adjust to the highest vacuum at idle, and then retard 1" of highest reading. Is this accurate, & should the vacuum advance be active or plugged during this procedure? (my advance is connected to a timmed port vacuum source.) 318 w/ edelbrock 4bbl., & mopar performance mid-range camshaft.
Thanks.