Here's a look at the general layout of the power supply. The filament and relay transformers are hidden under the control PC board and fan. Regulator IC's are mounted to the fan support brackets, and receive plenty of airflow. The fan expels through a vent in the top cover (not shown).
Not yet drilled at the time of this picture are the air intake holes, placed in the side panel next to the power transformer on the left. The large open space in the lower right will house the coolant reservoir and pump, whenever I get around to putting it in there.
One could certainly eliminate the variac; I put it in because I had no idea the amplifier was going to operate so well at 2kv; I was expecting to run it at 1600-1800v per recommendations, and my power transformer wasn't a perfect fit. But it turns out that the only thing in the entire system that is heating up at max output is the driven element on my antenna.