I've had this Mills open-front for about 4 years now. This was made sometime in the mid 60's. There's a thread on this here somewhere...
Anyway, the cash box, well more of a cash drawer - never locked; it just kept binding up and I never got around to it. There are two locks on each side and I'm sure they're original. Last night, after a shot of brandy, and a glass of wine, it finally got to me!
I pulled the drawer out, dumped a TON of quarters in another slot tray, and took it to the garage. The cam on one lock hit the side and the cam on the other went through the tray but hit the side of the notch where it goes into. So I spend about fifteen minutes filing the metal plates that cover the notch on one side and then filed a bit of the wood portion on the case. Then I took off both cams and hammered them (oh so gently) so they both had a slight arc which made them easily "go in the holes" so to speak.
Works great! Now I can lock the cash drawer for absolutely no reason whatsoever, but that's what I enjoy doing: making stuff work like it's supposed to.