I'll check it out. I measured the kingpin on my other trailer and it was 3 inches diameter.
The kingpin diameter is measured at the smalest part of the shaft so I think yours that you measured on your other trailer is a 2" . I am not aware of a 3" kingpin. The sizes jump from 2" to 3.5"
Also, I looked at my XM747 and it would be a very big job to change out the kingpin on that trailer. It is all welded in to the fifth wheel plate and covered with cross members.
The fifthwheel hight is supposed to be 65" and remember that the trailer has a folding, not a crank type landing gear. That means, that if your truck is not tall enough to lift the trailer of the landing gear, when backing under it, you will not be able to retract the gear!
The width of the trailer can be reduced to 120" by taking off the outer wheels, but be aware that it uses the hub piloted type wheels that are both held in place with just the outer lug nuts. (So you can't just drive the inners on a block to remove the outers)
Hope this helps, I know this trailer in and out, so feel free to call me if you have any questions (505) 787-9961
Soni