Well, I'm about done here. The preamp is quiet and sounds great. I purchased some Bendix 5992s on eBay for a good price, and they are excellent. The last piece is a 6.3 in > 6.3 out filament regulator board from a fellow at DIY Audio. Hoping to squash that last miniscule bit of noise.
I've got a fancy Hammond chassis on the way, and a can for the toroid, which I hope will shield it enough to place it on the main chassis. If not, I'll outboard the raw DC supplies. It wasn't a cheap project--someone more skilled at building reg'd supplies etc. could do it much cheaper, but honestly the Neurochrome board is kind of key to the excellence of the sound, IMO, as well as keeping the power supply fast and light-weight. Looking forward to it sounding even better when I get it off the sprawling breadboard.