Using vacuum gauge to tune engine?

"Depends". Different engine builds "want" different timing, a hot cam, etc, but you can not just "pick" numbers because of the curve in your dist. The engine may "want" more at idle (initial) but if you are driving it you don't want it to over--advance, so you may have to adjust it for max performance at high RPM and "put up with" less than optimum at idle.

The answer..........recurve the dist.

But since you seem to be trying to get it to idle, I didn't bother you with all that.

So what you need to do is find out where it needs initial / low RPM, and find out what it wants under full power/ mid-high RPM, then take those figures and recurve the dist. to suit.