Mild 318 pinging

So if I'm reading the charts you provided correctly, I actually slowed down the lower end of the curve with my advance spring magic
Here's the timing you measured overlayed onto the factory and it shows the advance from 750 to 1400 rpm was slower.
upload_2022-5-15_16-5-36.png

really should re-install the long loop spring before going any farther.
Yes well Maybe.
Depends on how the governer was modified. There's some adjustment in the spring perches, but not a lot.
If the inside of the slots was welded, then yes that would get it close.
If the outside of the slots were welded, then maybe it will be OK with less initial.

If you have time drive at little with vacuum advance hose plugged and see if its ok under what conditions.

As far as vacuum advance, rig a vacuum gage so you can see what the vac reading is when you are taking the timing measurement.
If you can do that in the garage, then also where you or a passenger can read it when driving steady at 50, and then 60 mph, you'll have pretty complete picture.

I pretty much spill the beans on how each item effects the advance in post 51 and 52
You can follow Rick working through an advance with a points type distributor here.
One difference is that with your combination, need to establish where it doesn't ping under load with the fuel you're using.