Um, 100 Watts into this amplifier set for "SSB", the high side should get you 1100 to 1200 Watts. More than enough if the tubes are throwing the normal 400 Watts of heat with no drive at all.
100 Watts into the "CW/Tune" side will get you closer to 700 Watts, plus or minus.
Set the carrier for the desired 200 Watt ( or so) carrier, then tune the Load control for max modulated peaks.
With the meter on "average", you will now probably see that the carrier level has changed. Peak the Plate Tune.
This is where one of two things happen. Either the knob was ALREADY set to that peak, in which case you are done.
-- Or --
You will see that the knob had to be moved a bit to reach that peak. If it had to move very much, you may now find that the peak modulated reading with the meter on "Peak" now shows a peak with the Load knob set slightly up or down from where it was. Set it to peak modulated power.
This is where "lather, rinse, repeat" comes to an end if the Plate Tune is now already at that peak carrier setting. If it has to be moved very much, lather, rinse, repeat until you find each knob ALREADY at the peak-power position. When you find this, you're done. Set the carrier for around 200 Watts, assuming you can get at least 700 Watts peak with audio.
And if you have it modified for higher bias voltage, this will reduce the tube heat on SSB side, and make it safe to use in SSB mode for AM.
The way it's built, that's not a safe thing to do. Gotta stick to Low (CW/Tune) if you want to use it for AM, so long as it is a stock unit.
73