Look for a 12A408 Thermostat Housing. They did fit them on some Morris Minors and some MG Models. They seem a little thin on the ground in the UK ?? but quite readily available in these parts;-
https://minisport.co...th-temp-adaptor
These take the stock Mini Temp sender.
Thread bump... Do you know if the Morris Minor equivalent used a different thread? Seen some posts online which state 3/8 BSP?