Starting advance with the vac-adv disconnected and plugged should be 8-12 (may even be on the factory sticker in front of the radiator)
4000 rpm with the vac-adv disc and plugged could be 36-38 maybe 40.

As far as the setting with the vac-adv connected... If it pings - retard it. In the mud there is no real need for vac advance as you are either in it to the rugs or idling. On the highway is when vac-adv makes sense and useable power.

I have always set as high as I can get away with w/o pinging and/or knocking during light acceleration, or at any time for that matter.
Pinging is a bad deal for a motor - like a little hammer hitting the top of the piston with every ping...