How to run RH807 at 400V?

[carbondated]

So I've decided to try out the RH807 as my second build, after the success of the RH84. It's almost the same circuit but with differently-rated components, and the choice of 807s, KT66, or 6V6 as output tube. Suggested voltage is 320-0-320 to produce a B+ of 350V. The author suggests it can be run with higher voltages, but with appropriate modifications... which he doesn't specify.

I'd like to run this with a 6L6 at around 400V, but (1) I have a Lundahl with 250, 48, and 250 windings. My first inclination is to use the 250+250 and drop this (high-wattage resistor voltage divider? but would that be detrimental to the sound?) somehow -- any suggestions? And (2) how much bigger would the choke have to be? Kitic adds just one more 10H/50mA to the RH84 power supply, but I suppose would be prudent to add another choke and capacitor (CLCLC) - say 20H/80mA and 200uF on each rail (or do I really have to split the two B+ rails?).

Here's the schematic: