> `-mode' functions don't usually take additional arguments to control
> setup, so I think having a defcustom here is fine.  I've applied your
> patch to the Emacs trunk.

As I noted earlier, a user found a bug in the display code when
editing files in hexl - the hex portion of the display would get
scrambled when the word size was <> 16 bits.

The attached patch should fix that problem.