Stock Thermostat for a 1974 250 4.1- 180 or 190?

[C10wip]

Could be due to a different sensor. I remember that getting the part number for the temp sensor was not so straightforward ( has been obsoleted and replaced or something ) and that there were a bunch of different resistance ranges which would then give different readings. I believe the one I used was AC Delco part number 2134793, from RockAuto.
The needle sits close to where I would expect it to on most vehicles so I assume it's the correct sensor; hardly scientific but that's what I'm going with now.

I don't know what the resistance range on mine is off hand, but if you can compare it to the one you have then maybe you can get an idea if we have the same sensor. Or, if you can't find out it out on paper, you could measure the sensor resistance when it's warmed up and compare that to mine. I think the resistance when cold is very high, i.e. not a useful number.

When I got my truck from the PO it had no thermostat, mud for coolant, a leaking water pump and a plugged radiator and heater core, and the temp gauge wouldn't come off zero which is why I replaced it ( and everything else ).