I have a piece of 3 inch channel welded to the upright. The flat sides are facing each other. There is about 3/4 of an inch between the two. Make sure you checkout the gussetts for strength. They also limitg how far onto the bucket the forks slide. I welded a large nut onto the top piece of channel after popping a hole with my plasma cutter. I welded to rods onto the top of the bolt in a V to turn it with. Takes longer to carry the forks to the tractor than it does to install them.
Ron
Ron