Proper assembly thermostat housings.

LovetheA's said
As I said in the original post the recession in the billet housing is noticeably bigger and the thermostat can move around and isn’t seated tight like in the oem housing.

I had used a newer thicker housing too and the thermostat did not seal well into the housing but it did not seem to be a problem.

Ultimately I bought a Classic Ind OE style and used the silicon gasket i mentioned above and have had no issues at all.