I can't Find The Correct Thermal Vacuum Switch Chevy 350

[Cadillac Kid]

Hello everyone. The original thermal vacuum switch (TVS) on my chevy 350 does not open anymore when It gets to temperature. I need a replacement. All of the replacements I can find are 3/8 in size. The hole in my thermostat housing is 3/4 in size. I even bought a replacement just for fun and the threads on the new (TVS) are way to small and it just sits loosely in the thermostat housing.

Where can I find a functioning (TVS) that has 3/4" threads?
I could bypass the switch but I would really rather have it working properly as intended. Does anyone have one for sale? My engine is a 1974 Chevy 350.

Thanks

-Gavin