Optimize the spark curve for a SlantSix.

timk225 said
I bought a timing light for the first time in over 20 years, just for this car.

You don't need the dialback. Its just convenient.

timk225 said
I'm running around 3-4 degrees initial advance of timing,

At what rpm?
Under 750 rpm it shouldn't matter, but it might depending on the distributor.

timk225 said
I think I hear it pinging at higher rpms under heavy load.

You will need to check timing at at those higher rpms.
Did I mention that a tach is needed?
Also you will have to mark the damper or make (or buy) timing tape for the damper. There is a "how to" article called Hillbilly timing tape. ;)

timk225 said
I have to wonder if it is getting too much advance from the weights and slots.

Not the slots or the weights. The heavy spring combined with a the light spring control the mid to high rpm advance. Unless your racing this 6 and running it higher than most sane people. LOL.