Found a partial answer to the sender question. That small sender is the fan controller temp switch Temp switch
At what temps it cuts on/off is still questionable. The threads are too small for the new sensor included in the kit I ordered so the new plan is to test and use it if it's GTG. It reads open now so it must go to ground when it hits it's designed temp mark.
It's cold and a rare snow day around here.
Dave

1949 Chevy 1/2-Ton 3100
1949 GMC 1/2-ton 100
In the Stovebolt Gallery
More pix on Photobucket
Video of the 216 running
Video of a Winter Cruise