I agree with Texas. During my searches, the best I've been able to come up with is a 3.90 gearset for the 54 and that was with a later model center section. A torch and welder can make just about any late model rearend fit under your truck. Your best bet would be to start looking under 3/4 and 1 ton vans. Most of them already have 3.73 or 3.55 gears. I don't thing converting to a 1/2 rear of the same era would be real viable due to the fact they are torque tube setups and your 3/4 ton is most likely not.
