Don't know why you would have two. Is the one on the head actually connected to anything?
Most people use the one on the neck if it's there (mine is just a blank boss). The one on the head will give faulty readings.
Do you have an electric fan? If so maybe one is connected to the fan and the other to the dummy light? Maybe gauge and dummy light?
No Chevy Inline came with an electric fan. They were either the fixed four-blade fan, or the later three blade clutch fan on the trucks. Yeah, my '78 Camaro with the 2nd version integrated head has two temp sensors as well. One in the bottom portion of the water neck (right next to the vacuum valve for the EGR and EVAP), and one in the cylinder head too. That seems to be the way they are set up in the integrated cylinder heads from at least 1977 onward. If someone with the '75-'76 integrated head could look and confirm if they have it too? I'm not sure on the '79 non-integrated 250 head in the Camaros, Novas, Caprices, and Impalas; or the 292 truck engines, was also the same way?