Depending on who you believe the old style triburner grate in the Channing II is rated from 5,000 at minimum fire to either 70,000 or 85,000 at maximum. I have owned several of the old style Alaska stoves and they are simple and and easy to operate. IMO they are better than the new ones with the paddles style feed mechanism.
Things to look for are cracking or erosion of the grate (an indication of overfiring) and that the stoker motor and convection fan work. There should be a couple rheostats with built in cords that go with the unit to regulate the output of the stoker and the convection fan as well.
Best of luck with your purchase.