this would, BTW allow the use of DH rectifiers like 5U4 and 5R4 w/o worrying about overvoltage-ing anything.

Try the 400V taps and get a raw supply of ~320v. plan on 50 mA through a dropping resistor to the reg tubes. looks like dropping 120V@50 mA. Ohm's Law to the rescue...2k4 and make it a 12 Watt WW( it's dissipating 6W in this app). So, from the filter cap, through the 2k4 resistor to our Node 1. from node 1 to ground, two 0C3 in series, with a 100k in parallel across the 'top' one. From Node 1 we attach the active plate loads ( the drain of the 'upper' mosfet, in the cascode version ).

Two more octal sockets, no big deal there. We get a 50 or so mA load for achievig critical current thorugh our L-C filter immediately. Two cool glowing purple-pink tubes.

Sound simple enough? you guys are getting complicated pretty fast. Best thing IMO would be hook up the PS to the 250 volt taps, and leave room for the gas tubes in Rev. 2( where you step up the ac voltage for providing the required headroom, and poke the holes in the chassis ).
regards,
Douglas