61 valiant heater valve

You really need the factory service manual. For a '61 Valiant that means a '60 Valiant FSM plus the '61 supplement. The heater valve on the '60-'62 Valiant-Lancer cars is mounted with two screws to a steel plate about 3" high by 6" wide. This plate is mounted with two screws to the fibreglass heater housing, which is mounted to the engine side of the firewall. The correct heater valve will cost you about $100 (such as here). A very similar valve was used on the Volvo 240 cars for many years, until that valve was discontinued and a different style service replacement was issued; that's this one, which costs less and is much more corrosion-resistant. Shouldn't be difficult to adapt the later type Volvo valve to your '61 Valiant; it comes with brackets and other bits to go in place of the earlier-style valve.