If installing a 47 fuel tank in a 49-53 truck you will need to replace one or two cross sills. The original 47 sill was notched to allow the tank to tuck up closer to the wood floor. Either notch your existing sill to accommodate the tank or use a repro or original cross sill for that application. Installing in a 54-55 will be a problem because the wood floor is about 2" lower and will cause the tank to hang well below the frame.
Mark
