1/2 and 3/4 ton B-series trucks came with the 218 CID 23” engines, and starting in 1950 were also available with the Fluid Drive option. The 1 ton trucks have the 230 CID engine and also had a FD option starting in ‘50. As I understand the car world, only the Plymouths use the 218 engine, and Fluid Drive was never an option for Plymouths. Any 23” 218 or 230 engine would be a direct replacement for the truck in question, but he’d need a 218 that was originally from a truck equipped with FD.
I am also curious why the engine is “beyond repair”. If it’s just a blown head gasket the head can be shaved to make it flat, block checked for flatness, and reassembled with a new gasket.