There is a COPS channel on YouTube which has over 60 educational videos on slots. Many of them go into great detail about how the machine works.
As I find time, I will list them individually here. Feel free to comment by replying to this thread.
Mills Roulette: https://www.youtube.com/watch?v=wjYgdU-k_-k
Caille Roulette: https://www.youtube.com/watch?v=ir7UvthZWkg&list=PLnyz3MPFaSygYGNjahewTWCq6b7hxDaDR&index=1
Midget Derby (only one known to exist): https://www.youtube.com/watch?v=xsCFyMWRzkY&index=3&list=PLnyz3MPFaSygYGNjahewTWCq6b7hxDaDR
Mills Duplex: https://www.youtube.com/watch?v=dN5Oue9WXf8&index=4&list=PLnyz3MPFaSygYGNjahewTWCq6b7hxDaDR
Caille Silver Cup: https://www.youtube.com/watch?v=c0C6Etqdz5M&index=18&list=PLnyz3MPFaSygYGNjahewTWCq6b7hxDaDR
Coochie Coochie (only one known to exist): https://www.youtube.com/watch?v=2LBWCwJ ... q6b7hxDaDR (sorry for the poor quality, this was filmed almost 20 years ago)
Buckley Bones: https://www.youtube.com/watch?v=JOZI0V5pvKs&index=28&list=PLnyz3MPFaSygYGNjahewTWCq6b7hxDaDR
Mills Roaring Lion arcade game: https://www.youtube.com/watch?v=AMKr-xGwUns&index=35&list=PLnyz3MPFaSygYGNjahewTWCq6b7hxDaDR
Watling Treasury: https://www.youtube.com/watch?v=D2m9XAandqw&index=36&list=PLnyz3MPFaSygYGNjahewTWCq6b7hxDaDR