From your diagram, on a M916A1 with 11:00R 20 tires (slightly taller than those issued with the truck), and the sliding 5th wheel fully to the rear you get the following:
A, the diagonal distance to mud flap corner is 74". When pulling the M172A1 trailer the TM says to slide 5th to the rear and remove the flaps, reducing the distance to 68". I've been pulling the 172A1 with the mud flaps in place with no clearance problems on tight turns. I also pull the XM974 lowbed trailer, using a king pin adapter again with no problems on the turns. Sliding the 5th to the rear seems to be the answer. It also helps in getting the pivot point for the trailer behind the center line of the bogie so that in backing up the trailer can be much more responsive to direction changes.
B, the distance to the rear winch platform is 67" and provides plenty of extra room for trailer neck.
C, height of the top of 5th wheel is 65". Again not a problem with a slight angle toward the rear for both trailers. The M172A1 is a match for the M916A1 and the more ordinary construction of the 974 also runs fine with its steeper angle.
You didn't mention the configuration of the trailer you were thinking about? Always seems to be a compromise between low deck height for ramp loading and good height for off the main road ground clearance and coupling height.
John