The Early Bronco axles are about 1 1/2" narrower, the rear axles perches DO NOT line up, but this is easily fixed, and the rear is a 28 spline. The 31 spline started in '78 models, which are also F-series based. I have this set-up under an '88 XJ, using the 9" drum brakes, and (ugh) 1.3" wheelspacer/adapters on it.