Greetings!
I looked up the Pincoil SFL 19-400/30-750 and the photo shows it rated at 28 volts.
http://www.marcospecialties.com/pinball-parts/SFL-19-400_30-7

The Williams 23-600/30-2600 coil on Marco's website shows it to be rated at 50 volts.
http://www.marcospecialties.com/pinball-parts/SFL-23-600_30-2

I would just buy a pair of new 23-600 coils/sleeves and do your rebuild from there. At least you are using the factory recommended part numbers. It seems that one was used on 25 volt flipper games around 1980 like Firepower and Black Knight. Then around 1984 they changed to the 50 volt coils for games like Pinbot, Sorcerer, and High Speed.

Well......(deep subject)....maybe the missing correct coil got old/swelled/hot and just broke so it got replaced with whatever was handy. Your other correct coil is even older and is starting to go out like the missing one did. So you have an old worn correct one and a newer incorrect one. Time to get two new correct coils and go buy a Black Knight for your 25 volt coil....lol. Good luck and post a photo or two of your game.