Over 65 ft

I have a f450 with a 40 ft gooseneck .my total length of unit is 66 ft bumper to bumper .is this illegal ?can I just get a permit in the states that I run for the year or should I just take the box off the truck .id like to keep it on .

 

I wasn't sure if I posted this in the wrong category.first time posting anything on these forums.if there's a better place to ask this ? I would appreciate it im under the understanding the 65 ft doesn't apply if the box is off cause it's consider a tractor at that point and u guys are allowed longer lengths

 

Thank you for your help.