Well I have just started collecting parts for my 813 project; so I will toss in my $0.02.
I would go with Mr. Willis's recomendations of running the tube somewhere around 900v @ 90mA. Your transformer would be more than enough to get you close. Notice though that this gives you somewhere around 35w in SE UL; so those 25w Edcors are not going to be enough.
Oddly enough, I had just emailed Edcor earlier this week to inquire how much it would cost to get a 50w version of those OPT's made. I'll keep you informed, as the more the merrier (and the cheaper !).
I've affixed my schematic. I haven't completely figured out the PSU's yet; but that is my goal in the next week. For B+ I am thinking of using 6D22S's, as they will supply more than enough current, and offer slow start. Naturally, I'd love to put in some 816's; but real estate concerns I think might keep them away (time delay, 5vct heater supply, etc). As far as the power transformer, I will be ordering the 550v toroid from Antek. It will give me 1.1kVct @ 300mA, and (2) 6.3@ 5A - all for the sum of $42/ea :D. I'll use the 6.3 lines to supply heat to the rectifiers and driver tube; while I will need an additional 15v @ 5A transformer for the heaters, as I think I will lose about 5v though the rectification/regulation.
On that note, I will be using a SS rect/regulation system for the heaters; paArt showed me a very nice schematic; once I get a copy I will post it here.
If anyone has suggestions on a PSU scheme, please let me know. It is a catch 22, as HV caps aren't cheap, nor are they small...But I guess that's kinda the point to begin with...hehe