I finally dragged my 5KVA/11KV UK pole transformer out of storage and painted it. I went with flat black because it looks cool, and because it reminds me of death--something to be mindful of when dealing with pole transformers. It looks much better now. The original gray paint was in bad condition and the case was rusting.
The data plate is faded and difficult to read, but I was able to glean some info from it. For one thing, this beast weighs 260 Lbs. I don't know if that is dry or wet weight. Also, the date of manufacture is 1963! Give the Brits their due--they built it to last. The transformer has four 240VAC taps labeled A1 through A4. The data plate lists three possible hookups for 11500VAC, 11000VAC, or 10500VAC. I selected 11.5KV.
I tried it out on the 4" coil with 9KW of hot water heater elements as ballast, and I was a little disappointed. The sparks are not any better than with the much smaller dual MOT power supply. Also, I had to close the gap a little to get reliable firing. The 9KV setting is too wide for it. The resistive ballast must be knocking my voltage into the dirt. In order to make use of the pole xfmr's full capability, I'll have to build a bigger tank cap. I'm thinking along the lines of 0.1uF instead of the .047uF I'm currently using.