Heavy Stirrup design using used municipal equipment cutting edge scrap...grader/plow blade.
Requires a heavy frame to mount to 3-pt, and grader blade 'stirrup' must be specially welded to suit the high carbon alloy...usually 1070-1090 steel.
Preheat, multiple passes with a low hydrogen rod such as 7018, 8018 11018, and post heat/slow cool. I use a milling machine to drill holes in the linking parts, and buy the pins at Tractor Supply, grade 8 bolts to attach the 'stirrup' at K.L. Jack.
Category 1 or 2 setup. Best to lay out the height of the unit with careful measurements of the tractor's hitch movement to make sure you get the right depth. Also it seems to help the depth issue by angling the bottom blade of the 'stirrup' about 5 degrees to make it cut and drive itself deeper. Most farm tractors don't have down pressure ability, and the bed lifter can work its way out of the ground without some way to keep it engaged in the soil. My use of massive I beam 8 x 28# helps.
Have not broken one yet in this rocky Maine soil. Units I've built have about 20 hrs labor and $50 in parts, mostly scavenged I beam 'drops' up to 4' wide. I've sold them, custom width and depth, for $300-$400
I have some Auto Cad drawings to share if you're interested.