The best reason that I had heard of was to not cause damage to the backglass.

I recant my previous comments. Should of waited to comment until I had the facts at hand.

Once again Spinal you have come up with an interesting question.

Sooo, from the 1972 Catalog on Page 12. "Shock Mounts for the Replay Units".

Exactly. Another precaution against cheating. Manufacturers often spring mounted or rubber mounted any assemblies or relays involving replay awards. This prevents slamming or other hard impacts from awarding free games illicitly.

It was those springs and 1 rubber grommet that prevented us yard apes from getting credits. When we use to pick up the end of the game and drop it an inch or two... Hmmmm. Such Bastiches we were.

One of the reasons the coin lockout coil exists. Every time the score motor operates, the coil turns off, and any coins deposited are returned. If the coin mech didn't work this way and a coin was inserted at the time the score motor is running, it would count extra credits.

I've also wondered about the credit unit mounting since I first opened up my KOD, along with why there is metal shielding on the side of the credit reel. Now this conversation makes me think that metal may also be an anti-cheat device to block access to the reel from a hole in the cabinet, is that the case?

Yes, it is.

Yes. In fact, some Williams machines had a metal box which encased the entire replay unit. They're usually missing though, because the first guy who ever had to service the unit would likely not bother to screw it back on afterwards.