No temp sensor hole in heads

[aggiegrad]

I have a low millage 68 gmc that everything appeared very original. 307, TH400 and even has all original shocks. I am trying to convert it to a gauge cluster as the aftermarket 3 gauge dash mount were all broken. I have prepped a new gauge cluster and purchased all oil lines and sending units to do the swap. However, I cant find the plug to screw the temp sender into. The green wire connector is laying across the intake manifold and a mechanical temp gauge line was added to the heater hose outlet in a pipe tee. I assumed I had a light sender or a plugged hole in the heads like every other picture I have seen but cant find it. I have felt the rear of the passenger side head between the rear two plugs and there is no threaded plug. I looked in the drivers side front two plugs and no hole there. I took pictures with the cell phone to confirm there is no hole in the head. Am I going crazy or is it possible that these heads were replaced sometime with ones without sending unit holes. My original intake doesn't have a spot either. If the heads were switched out they kept all of the other original parts still on it. I recently bought this truck from the 87 year old that owned this truck the whole time.


thanks for information.