Aha!

I ordered some parts I don't need.

I thought that one would wish to have the peaking gap (an untriggered gap switch on the output of my Marx generator intended to sharpen rise time of the output pulse) fire last. While that is true, the way I intended to ensure it was wrong. I made the peaking gap electrodes larger in radius (increases firing voltage) and a bit further apart (increases firing voltage).

It turns out that -- for complicated reasons I won't go into here -- the savvy designer wants SMALL diameter electrodes and surprisingly SHORT gap distances for peaking gaps on the end of Marx generators.

"The generation of 50pS pulses with a 60kV charge in a single channel switch of very small dimensions has been reported in 'Ultrafast Gas Switching Experiments', Proc. 9th IEEE Pulsed Power Conference, pp.491-494, 1993."

Which paper I have subsequently dug up, but not read yet. 60kV in 50 fucking picoseconds? Unpossible!

So I wasted a few bucks, but the thing has just become quite a bit simpler to construct. I do have to rework my models though.