Not sure if you are looking for a quick detatch (QD) and one that is almost unnoticable when not in use type deal, but I made one for my lighweight wrecker over 20 years ago. The drop frame hangs from the pintol hitch then bolt on braces go forward and up to brackets permanently fixed on the frame. When removed, there is almost nothing visible from the rear.
I'm sure it can be scaled up appropriately but the sketch below is an approximation.
View attachment 404910
The diagonal braces naturally need to be very rigid and resistant to compression - hence the tube in the diag.
I am not familiar with the underware on a M931/2, but I'm sure a little ingenuity could be applied and appropriate brackets could be fab'd.
Hopefully this has given food for thought.