Go to your local auto parts store and ask them to compare front wheel bearings from a 90 Ramcharger to an 84 Ramcharger. If it's the same bearings, ask the same about rotor diameter. If those are the same, buy new rotors, bearings and brake pads and rock on! I'm going the opposite direction with my 88 D100. It has 5.5 bolt pattern on it, and I am installing an 8 3/4 out of a 72ish half ton. I bought a pair of axles from a 74 Power Wagon 8 3/4 with 5.5 bolt pattern. I'm going to swap them into the housing and use the existing back brakes on the truck.