Phil the factory method of setting timing on the B20 with vacuum retard is to set the initial timing with the vacuum disconnected. To set 10 degrees BTDC with it connected would produce a total advance of over 40 degrees, which is far too much.
Ported vacuum advance, like old Fords, can be set connected or disconnected as there is no vacuum signal at idle. GM and Chrysler are disconnected because they use manifold and the vacuum is present at idle. Exceptions exist in all by the time emission controls happened by though.