So, now I know why the previous owner never replaced the thermostat, lol. The head of one of the mounting bolts is busted off. It's funny thinking about it because he gave me a new thermostat and I wondered why HE did not install it. It is the top right bolt if you're looking from the front of the car. How do I remove the Thermostat housing now? Should I undo all the other bolts, pry off the gasket and turn the whole thing in a counter-clockwise direction??? Or will that not work? Or maybe there's an easier way to do it?

I have a way to do that.
The Thermostat housing and the
cooling plenum are 2 separate parts.
You could remove the 3 nuts off the
plenum and remove the whole thing.

Depending on where the bolt is snapped off,
you can either replace the whole unit or maybe
just drill out the remainder of the stud.

I have purchased a new plenum and Thermostat
housing. I have 2 spares to give away for shipping.
They are both old and have some pitting.

One is better than the other.

It will be nearly 100 bucks to get a new plenum
and housing and T-stat.

I am doing a complete cooling system-ectomy so I have
plenty of parts here.