Power supply

I installed the 15 henry choke.  That brought the voltage right down into the 180-200 volt range.  I hooked up a current meter and was seeing around 46 mA with one nixie connected.  That told me that the regulation tubes were pulling a little too much current.  I needed to add a little more series resistance. 
I recalculated the series resistor and came up with a value around 200 ohms.  I just happened to find a nice 5 watt ceramic 220 ohm resistor.  Putting that in the circuit dropped the current down to about 36mA.  Right in the ballpark!
Now the voltage regulation tubes are not super hot.  You can even touch them after several minutes of operation and not get burned.
Everything is still temporarily wired for now.  Later I'll mount the choke on the top of the board and run the wires better.