nice, my radiator hose coming off the bottom was in the way of the box on mine, i wonder if maybe you have a different engine or radiator? mine is the 4.0. and im still running stock steering, with unbalanced 37s and without an alignment, so needless to say its pretty shaky. when i aired my tires down to 8 lbs psi it handled a lot better, so if youre running fully blown up tires that could be why its unstable. but thats just a quick fix till you can get your casters put in and get it aligned, hopefully that will take care of it!
and if you have any pictures of your steering box mounted, id like to see what you did