I guess it works different for various engine combos. However, my dsitributor is supposed to be the same one used on the ZZ4 base motor and I use manifold vacuum for the vacuum advance line. I have a 350 with Blueprint 64cc aluminum heads and use about 15-16 degrees base timing and 20 degrees mechanical. My cam is 213/217 @ .050. AFR runs about 13 at idle, but jumps around a bit. At cruise its usually about 15.5-15.9. Getting stable AFR with an old Quadrajet has been challenging.
I did switch to a vacuum can with less total advance (around 14-15), since the original gave me about 22 degrees advance. I've always been told that not running vacuum advance will really lower highway gas mileage. I use 87 octane gas and have heard no pinging.
Bruce