Your setup is a little different than the original poster - he has a Vortec small block.
On your TBI big block, the one in the intake near the thermostat is for the computer input. This is the only sensor on your TBI engine that tells the computer the coolant temperature.
The one on the driver's side head is for the dash gauge.
The one on the passenger side head is for the auxiliary fan that should be mounted ahead of the A/C condensor.
(By the way the Vortec big blocks are pretty much set up the same way though they have the IAT of course in the air intake tube.)
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Richard