Temp sending unit for '68

[Mark McDonald <tomswift@xxxxxxxxxxxxx>]

I am having a devil of a time finding a new coolant sending unit for my
'68.  I hope I am looking at the right part.  If you are facing the
engine, it is located about 2" to the left of the thermostat, between 2
heater hoses.  It looks almost like the bottom of a lightbulb with a
hexagonal collar on it.  Above the collar is a small cylinder with 2
blade connectors set at right angles to each other.  The dimension of
the hex collar is 15/16".

I have gone to 4 different parts stores here and they either don't even
have a number for this part, or what they do have is way too small.  Pep
boys had it-- according to their computer-- but the part is about 1/3
the size of the thing on my car.  Is what I am looking at a housing?  In
other words, if I take it apart will I find the sensor inside this
thing?  I am pretty sure I am looking at the right thing, because when I
disconnect it my gauge goes dead.

I am trying to replace this because my gauge never gets up to normal.  I
tested the temp of the antifreeze in the radiator and it got up to about
150 degrees after about 20 min. idling in my drive.  That would seem to
be close to normal temp (?), but the gauge never moved above about 1/4
of the way over toward the center.

I do not think the thermostat is the problem, because when I start the
engine cold and look in the radiator I do not see instant circulation of
antifreeze, as you would expect with a thermostat that was stuck open.
So I thought maybe the sending unit was bad . . .

But I cannot locate a sending unit.  Can anyone help?

Thanks, Mark