I know it's blasphemy, but since Karl is already going to hell for putting sand in your tube pre, what about regulators? Paul Hynes makes some nice ones. His shunt reg specs are incredible - PSRR is 110dB, Zout 2mOhms! Noise .5nV, settling 50nS.
I think you could use only one for shared (stereo) B+, it's fast enough to make 20mA for two 26s without crosstalk. It's 5uS between samples at 192kHz, this reg
settles 100 times faster! You're probably sharing B+ now anyway? Then another one for both heaters. Byebye hum. The low impedance will allow the tube play as strong as it possibly can, bass impact, etc.
If Karl needs a specific voltage on B+ then you might need to buy a new transformer, but you can ditch the big storage and chokes. If you can donate 10V to the regulator then you can use the PS you already have. 2 regs + current sources about $450. They run hot so they need some air, or heatsink if you reduce the voltage very far below input, but you won't have that problem. They can probably bolt to the bottom of your case, if you have the room...
http://www.paulhynesdesign.com/Then Karl can light up the heaters in a dummy big bottle rectifier tube on top as a disguise....
