Hi Jim,
Since you now have access to all the secondary leads, one option would
be to reconfigure your power supply using the existing wye (or star)
primary, and convert the secondary to delta configuration. If the
original wye-connected secondary could deliver 24 kVDC, changing the
secondary to a delta connection will result in an output that is
1/sqrt(3) times the original output, or about 58% of the original
output. The revised output will be 0.58*24 kV or about 14 kV. You can
then connect six diode strings to create a FWB DC output. This is now
in a reasonable voltage range for either direct operation or 2X tank cap
voltage multiplication using either resonant charging or a
charge-reversing (Steve Young) gap. This configuration will also provide
you with 58% higher output current (for the same transformer kVA output).
Bert