So you replaced the thermostat and then it went up to 210, so what is the problem? 210 is not a problem when you have at least a 4lb cap and a 50/50 anti freeze mix. You said it moved down after you started moving so I wouldn't be at all concerned at this point.

1953 Chevrolet 3100
261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done
In the DITY Gallery
Video of the 261 running

1964 GMC 1000
305 Big Block V6, sm420, the next cab off restoration