FYI, the Doyle book lists the Tremolo options of the JTM45 head as: model T1987 and T1989
With the 1989 being marketed for organs. The catalog picture with the models is on page 165 of the first edition of Doyle's book.
Btw, you don't necessarily have to get the 12W Mills. they are pretty big. But the 12w and 10w are good for 1000Vrms. If you aren't familiar with Mills, they are what lots of manufacturers and hobbyists use for high quality speaker crossovers.
FYI, The Leak TL/25 Plus Stereo 50, which is a legendary HiFi amp that used KT-66's, had on OT with 7k primary and screen tap at 49%.
Heathkit used two different Peerless transforms for its W5m, the first had a 10k primary and the second was a 5k primary OT.
Everything depends on the bias tap...
Joe, those EI KT-90's are extremely desired by hifi folks that specifically have the Harmon Kardon Citation II. If you ever need some money, you could make a nice profit. As far as guitar use, I see no point in using them; they don't bring anything to the table that a new KT88 or 6550 has.