Torque box? Frame stiffener you mean? Where and why- no reason to do this especially with a Coyote.
No reason to at all. Bronco frames are boxed and very stout.
Also, people think Coyotes are the most powerful engine on earth- they aren't. There's guys who have big block FE's, 460's, 351C's... all these make more HP/torque than a Coyote and nobody's had any frame issues.
Want to twist something up? Put a gear doubler behind the trans, put low gears in the tcase, put high numerical number gears in the frt/rear diff's, put 100% lockable diff's frt/rear, put 40" tires on. ALL these things multiply torque & transfer torque to the grouond many times over what the original Bronco could ever dream of putting to the ground. Street driven Coyote motor powered EB will never see anything within 20% of the torque generated and transferred to the rocks like a rock crawler EB equipped with the mod's described above.
Short version? No, you don't need it.