We looked at one like that before we got our GT325. I was very concerned about the tail overhang and the possible overloading of the rear axle and we decided not to buy.
If it's a digital odometer, you might want to check with Ford (assuming it's an F450) for either a hidden selector switch or a jumper wire somewhere in the indicator circuit that will switch between KM and miles. I'm sure the instrumentation is the same for both markets, as there are other Fords where you can actually select it from the panel.
Frank and Eileen
No longer RVers or FR owners