Here is the site the 78buckshot was referring to. Lots of good information on it. Not sure that the site will have that specific info (WMS to WMS) however. Can't hurt to take a look.
[on edit] The closest thing available to WMS-WMS dimension is front axle tread (center of tire to center of tire) which is 60-9/32 inches pe the Vehicle Info Kit. You could get pretty close by checking if the wheels have any offset and allowing for that. But that would still be off a little because of the camber of the front wheels (closer on the bottom than the top.)
