The "sending unit" isn't a separate item- - - -it's incorporated into the gauge with a capillary tube that can't be replaced separately. There's a liquid in the sending bulb that evaporates and moves the temp needle with vapor pressure- - - -no electricity involved. It might be possible to get the gauge rebuilt to original specifications by a professional restorer.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!