Hi Ricardo, yep, double nut is the standard way to get studs out. Glad you got it back to what the factory intended, both with the correct bolt and with a t-stat and proper o-ring and gasket.
The only issues you are likely to find from running the truck with no t-stat are extra carbon deposits in the combustion chambers and exhaust from running too cool for too long. Not a major worry, but that's about it. Happy cruisin'!