The ubiquitous round “in cab” Smiths heater has been used on a myriad of British cars. Jaguar, Morris Minor, Triumph, AC and Land Rover…. to name but a few.
The heater takes a hot water feed (operated by a tap on the cylinder head… as you do) from the engine into the heater matrix. The front face of which carries a fan that pushes cool air through the hot matrix; thus distributes less cool air around the cab, or…. by way of two flaps on the front of the unit, air is “forced” through the ductwork and onto the windscreen, where it will no doubt decrease the drivers visibility 😉
The heater motor is operated by a rheostat (potentiometer) switch, allowing control of the fan speed… depending on the drivers need to hold a conversation.
The entire unit was stripped and repainted (including new “ironmongery” and manufactures badge) some months ago (I didn’t take any photos) and having tested the motor is back together again.