Make sure it seals properly, or you have some type of gasket set up, if you run it without one. The thermostat could easily be the gasket to keep coolant from leaking around it's housing. As for a 75 mile trip without one. If it seals fine, just give it plenty of time to reach operating temperatures. Especially if it's in the cold weather.

All in all though, the healthiest for the vehicle would be to just replace it where it is, they are very straight forward and easily accessible.