Ohhh OK.... ya.. gotta have a mower!!
Another idea for you.... Make the bracket that mounts on the tractor "L" shapped. Mount the pivit on the top of the L, and have the lower end of the L sit in a channel. Make the hight adjuster on the deck itself, that way when you lower the deck, it will bottom out, and you will always be at the preset hight. The channel holding the lower part of the mount, and the higher upper mount, will make the pivit a little more stable to twisting forses.