On the Advance Design trucks, the 3/4 tons used a partial torque tube. The torque tube on those only went from the transmission to the carrier bearing, then from the carrier bearing back is an open drive like the 1 tons and your '59. The rear diff will be the same HO52 as the later 3/4 tons. The 4.11 3rd member that the seller mentions would have come from a '68-'72 3/4 ton, which is a direct interchange.
