Hy 1fletch, the 41 and 54 bellhousings have different tranny mounting patterns, and different engine mounting surfaces/angles, but they can be interchanged. A 12 volt flywheel has a different number of teeth on the ring gear than a 6 volt flywheel, so other than using a car 6 volt solenoid starter, you would have to change to a 12 volt flywheel. Your 41 flywheel probably has a clutch retained by 9 bolts, and I believe the 12 volt flywheels are drilled for a 6 bolt clutch retention pattern. Swapping stuff back and forth to make the new engine work in the old truck is doable, but it depends just how you want to equip the old truck, how much to swap. Hope that helps.
