Bally flipper coils are parallel wound, just like the later Williams flipper coils. I unspooled one of them to verify this - there are 2 separate coil windings in the coil, with the hold coil first, then the primary coil closest to the bobbin. So any benefit to the flipper cap WMS uses will benefit the Bally cap as well.

Well, Bally/Stern coils are 43 volts so not that much less than Williams.

The parallel winding on Bally coils I unwound one myself. They are 2 separate coils on the same bobbin, hence why they also have 4 wires to 3 terminals, and 2 diodes. Just like Williams later patented (great that people can patent preexisting tech). The info about parallel vs. series was from Clay's old guides/videos - he made one where he put the caps on the series wound and said it didn't decrease arcing, but in the video you can plainly see that it did.

I don't have a large problem with the pitting so I don't really worry about it on games that originally didn't have them.

Apparently. I guess in an arcade or heavy play situation it might be good to have.

I guess the theory is that a back EMF spark is a back EMF spark it doesn't really matter what kind of coil it comes from either will wear away the EOS contact.

Most people solder them on

The EOS bracket was originally taller to accommodate zip tying the cap to it, with a couple holes drilled in it to hold the zip tie. As noted, no resistors were used so it will be interesting to see what comes of your experiment with them.