Re: New project 1975 Ford 5000
The doohickey is a telescoping stabilizer. The reason for the slotted pin hole is when you want the attachment to be free to move a limited amount. Most commonly used with a moldboard plow.
I prefer telescoping stabilizers over chains. I commonly use a Brush Cutter, Flail Mower, BB, rear blade, dirt scoop and tree puller. All of these I want held in a fixed position. The telescoping stabilizers allow this restriction easily. Hitch up the attachment. Lift it. Move it to the spot you like. Pin it in place. No tools or hassles required.