160 degree thermostat (starts opening at 157 and fully open at 180).
http://chevy.oldcarmanualproject.com/chevyresto/56160.htm

You should use a gasket between the carburetor and the insulator, especially if there is no "cutout" in the top surface of the insulator for a vacuum port.
If there is a "cutout" in the top surface of the insulator, you may be able to use no gasket.
You can get away with no gasket between the insulator and the intake manifold, unless you get a leak there.

I use a gasket in both locations.
I have never had a leak.

Tim
1954Advance-Design.com
1954 3106 Carryall Suburban
1954 3104 5-window pickup w/Hydra-Matic
The 216 and early 235 engines are not "splash oilers" -- this is a splash oiler.