I've recently been working on getting locks installed on my cabs as well. They definitely vary, but most coin doors use either 5/8" or 7/8". The back doors seem to use 7/8" or 1-1/8". I'm pretty much just getting locks on the coin doors for now... a lot of the back doors are screwed shut, and that doesn't really bother me.
In a lot of cases you can get away with any size lock that's at least as long as you need (i.e. you can't use 5/8" on a cab with a 3/4" thick back door, but can use 7/8" or 1-1/8"), since you can bend the cam (some come bent for this purpose).
Sometimes a lock will hit what's behind it though, and you need to install the correct length (Nintendo coin doors come to mind, which hit the wooden coin bucket with a long lock).
DogP