By chance I just walked in the door after completing a rear fork adapter for my Harbor Freight Quick Hitch. See attached photos.
The fork material was left over from a standard 'relay rack' that I previously made bucket forks from. (a 6 ft tall radio transmitter chassis in its first life). The channel may seem upside down here but it's stronger with the thin edge in tension rather than compression.
The sloping angle iron is old rusty bedframe, and the only new material is that $3 horizontal angle iron that carries the weight on the 3-point pockets.
In the second picture it easily lifted a 485 lb box blade with half that weight 2 ft back, and the rear half on the tip of only one fork.
This is sufficient capacity for my application. I built it to put a platform on, and then carry several garbage cans of water down to new trees in the back of the orchard.
Maybe this will give you some ideas for building one.