The temperature sending unit is definitely not the factory unit.
I don't see the speedo cable in any of the pictures.
We are beyond my scope of knowledge electrically. I sent a PM to VetteVet to see if he'll chime in on this discussion. He's our resident electrical expert. In the meantime here is a link to a color coded wiring diagram in case you haven't seen it.
http://67-72chevytrucks.com/vboard/s...d.php?t=185856