Vacuum Advance Adjustment Question

[68 P.O.S.]

Hey all. I’m in the process of setting up the ignition curve properly on my 72’s 350 and the vac advance is my last step. I’m installing the Crane 96600-1 adjustable vacuum advance kit and my question is, how many turns should I adjust the vac can since I have 20” of vac at idle? I’ve done a ton of research and found a lot of great info on timing, but not so much for this vac can. The directions don’t give much info either; other than insert the allen wrench, turn fully clockwise, test drive and adjust counter-clockwise for ping...rinse, lather, repeat. I guess I’m looking for a ballpark number so I get close, then fine tune from there. Anyone care to share? Thanks in advance!