I think there’s maybe one cure for you: http://www.nemesisnxt.com/kit/p3-2.php

Early Broncos (‘66-’77) are tough to beat. They will last forever. All you really have to do to the worst of them is cut out the floor pans, weld in new ones and drop a new motor & tranny in. Also, put some polyurethane bushings and mounts in and you’re set.