Sounds like your 40 may well have a 59A engine in it. If so, the Stant 14157 thermostat that was made for the 1990 Subaru Justy fits perfectly and is higher flow than any other that fits your car. Here's why:
https://www.fordbarn.com/forum/showthread.php?t=143576
Sold by NAPA as part number THM 111, or O'Reilly part number 2962 which is also Murray part number 4157. All the same stat. The original style thermostat is Ford part number 11A 8575 B and is sold by C&G here:
http://cgfordparts.com/ufolder/cgcat...&sp=Search+%23 But is a lower flow than the Stant one.
Here are other threads on the topic:
https://www.fordbarn.com/forum/showthread.php?t=112889
https://www.fordbarn.com/forum/showthread.php?t=113366
https://www.fordbarn.com/forum/showthread.php?t=113979
P.S. Don't use the rubber gasket that the Stant stat comes with. It just rolls off and jams up. Just take it off and chuck it before installing the stat. Also, to secure the stat from pushing up, turning 90° and not working, secure it with one very thin strand of stranded wire as follows:
.