The 1N3710's are 200V zeners in places I'm used to see ordinary switching diodes. Where'd you find this configuration?
I'd also expect the relatively low voltage varistor across the BU to dampen the HV too much. How about placing two of them in series?
I've found it where I found the calculator for the snubber component, i.e. http://www.daycounter.com/Calculators/Snubbers/Snubber-Design-Calculator.phtml , and I was pretty sure those were zener symbol! If simple switching diode would do I'll put some 200V 3A in place.
As for the BU's varistor, I assume two 240V in series act as one 480V?
Thanks.