The bronco's a really high body in the rear, I'm thinking you're gonna have to fab something up yourself. A simple way I could see is to cut the support posts in half, and extend them by screwing small metal plates on both sides through the post holes. The holes are kinda small so you might have to drill them out a little, but not too much or they'll break too easily. If you can find aluminum tube that fits snugly around the mount posts, that would be even easier, then you just drill holes in the tube and secure it with pins. But I'm not sure alu tubing comes in such small diameters.