[davepl]

Geezer won't like me saying it, but your vacuum advance should be connected to ported vacuum (above the throttle blades), not manifold vacuum. And when properly connected like that, it will not cause any advance during cranking.

If your truck runs "good" at 12 initial, keep it that way, but you might need to have your distributor recurved to lock out some centrifugal, or you could wind up with too much total advance.

If you do run manifold vacuum to the vacuum advance it'll advance at idle (and during cranking a little too) and you'd run less initial advance. I would postulate that 12 initial PLUS vacuum would be way too much.