I have an Early Bronco with a fresh 393W. I currently run a NP435 granny 4spd, but have a C4 that I'm wanting to build and swap in. The C4 is an early Bronco model out of my 77 parts rig. I want to build a stout tranny that can live at low speeds on the trail and take 400 ft/lbs of torque. What mods are recommended?