Here's a comparison of the sound boards (Charles Kline photo), from back when I was troubleshooting mine:
https://forums.arcade-museum.com/threads/bally-sente-soundboard-troubleshooting-acia-time-out.505124/#post-4493842
Could probably get away with using RC car pinion gears, double check measurements.
https://www.amazon.com/RiToEasysports-Motor-Pinion-Compatible-Traxxas/dp/B093SQ95KT