Ya know, it just occurred to me another even cheaper idea... If a person replumbed the rear brakes and tied the two left rears together on a circuit and the two right rears together on a circuit, you could use a momentary switch to the line lock on each circuit to hold pressure off one side or the other. Then pressing gently on the brake pedal would stop the spinning tires, and transfer some torque to the wheels with traction that weren't spinning.... Ok, might need three line locks... One fed via diodes so if either rear gets excited, you don't put pressure on the front brakes... But I bet you'd see noticable improvement even without limiting front pressure... Just add enough brake to get you moving again... I used to do that even with no linelocks and two open diffs, just add some brake pressure to get the left to right torques closer to equal... Many times, it'll get you through!!
Voila, Poor Man's Brake Traction Control... "Yeah, my deuce has PMBTC... It's unstoppable!!"
C