Excellent work! I appreciate Richard's comment about the diodes not being a limiting factor and also that Spellman would have been designed to have a very low % ripple which is not necessary. Given it is a charge pump circuit i think the factor determining how much power it can supply is the capacitance of the capacitors in the stack (i.e. can be estimated from the charge CV^2/2)
Joe, I'm sure anyone else trying to rig this up would appreciate any further details on the driver and/or the pinout etc of input to the Spellman HV stack, especially for those not so expert.
BR
Chris