If this is an unmodified BC-610, run it at specs. The only concern is excessive tube color. If at resonance and full output, the tube color all but disappears, forget it.
The BC-610 was without a doubt (in my opinion anyway) was the biggest, heaviest transmitter ever built for military work. I think the expression, "built like a battleship" originated with the 610!
The T368 was another military monster.