It looks like the latch assembly ($78) is cheaper than the latch ($92) itself.

Buy the rear hitch, telescoping hitch, latch assembly, and stop block for $517 and provide a 3/4" pin and a couple 5/8x1-1/4 bolts  or complete assembly for $868.

I never looked much at the Unverferth wagons, but they appear to be very similar to the Deere 1065/1075/740 wagons.