A M931 with G177 radial tires barely clears the 146 landing gear. In fact, if you put the the landing gear all the way up, where they are even with the widest part of the tire, they will rub on the tires in a turn. Forget about trying to have the mudflaps on the tractor while you're using this trailer.
As mentioned, taller tires on the trailer should help a bit, making the landing gear angle a bit less, moving them away from the tires and lessening the stress on the kingpin as well.
I didn't consider tying the feet up to gain more clearance. I'll have to try that next time. I will be moving a M146 with M931 w/G177s soon, I will get some photos.