Hi Roger
I cured my car (1938) by making a Dipstick and carrying it in the boot, sorry not much help technically. Seemingly you can not get a Sender for a prewar car, just not available. About a year ago Chris from TOC Spares said he was working to try and resolve by modifying a similar sender from an old Austin.
Not much help (useless I guess) but thought I’d share anyway
Davy
David Selfridge