Your calculations appear correct to me. I'll comment on the temperature rise issue:
The temperature rise of a transformer is related to the insulation system of the coils, and is the temperature rise of the hottest point (or presumed hottest point) of the coil at full load operation. The temperature of the outside of the can or enclosure gives you very little clue of what is going on _inside_, and it is the temperature _inside_ that you care about.
I am not familiar with any easy way to test such temperatures in the field; I do electric motor research, and we have our motors built up with embedded RTD temperature sensors.
-Jon
