Hi !
Fast Draw Gottlieb is a very pleasant game. However, there's no Extra Ball ! It's a pity !
Using my brain, I built this function on my own game. Here's a link wich will help you to add this function with many details.
Best regards
Daniel
https://www.retro-flip.com/t11179-Rajout-de-l-Extra-Ball-sur-le-Fast-Draw-Version-electroniqu.htm