I put a ‘Taxi heater control valve’ on my ‘82 4/4.
It seems to work fine.

£14.50 on eBay.

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F202736344035


Don

1982 4/4 4 seater