The Black Beauty and Blue Bell are probably from the mid to late 40's. The Castle front is mid late 30's (I think) and the Jennings Chief could be 40's early 50's I believe.
What did you pay for them?
Are any in operating condition?
For starters, in MANY cases, the escalators get jammed. (That's the part in the clear window above).
Don't force or oil anything until you know a little more on mechanical slot machines. Escalator rebuilds are easy long as your willing to get a little dirty. It's a matter of cleaning them and replacing the springs which you will get from Dave Berten but his website is down right now. He's one of the few that sell a multitude of parts for antique slots.
As much as this is a awesome site for slots, it's not the best for mechanical machines. Still there's a few members that might reply so don't leave us.
But, I HIGHLY going to
http://coinopcollectorforum.com and post in the appropriate section. There's a 90% chance Monti will reply! He and the others are full of knowledge on mechanical slots.
As for value I'd guess the Jennings and the Mills Castle front are more valuable but wait til you hear from the guys on the other forum unless some of our very few mechanical slot experts reply here. They all appear original to me. If you had a Mills Golden Nugget though, there'd be a good chance it was a repo.