I continued the long resistor hunt, and did find some bad ones. This pair of 82K/2W resistors should measure 41K, not 122K:
Most of the other 2W resistors look like a different brand -- the usual dark colors -- and they looked pretty good, but many got replaced anyway.
After those replacements, the voltages on the 12BH7 demodulator looked closer to normal. The voltages on the grids reflect the amplitude of the signals coming from T115, the 3.58-MHz transformer, so when you adjust T115 in the course of alignment, they also change.
At that point, I had basically the same issue -- colors in the color bar pattern were incorrect, and no amount of adjustment made them right.
The replacement 3.58-HMz transformer had produced reasonable-looking waveforms in the breadboard circuit, so I decided to pull out the old transformer and try it.
Comparing the transformers side by side renewed my doubts. The new transformer has a lot more windings, closer together. Remember, it also has 680-ohm resistors in parallel with each capacitor, and the capacitors are 1500 pf, not 1200 pf as in the original.
The new transformer fits physically, but I had to reroute a couple of connections, since its output to the phase detector is terminal D rather than F, etc.
(After installing it, I did reattach that hanging blue wire, seen in a previous photo running across the installation site.)
The bad news is that it doesn't work -- not even close. I ran through the color AFC alignment procedure and tried other cowboy adjustments while watching the screen, but one of the waveforms coming out of the transformer is very irregular and the two signals are badly mismatched in amplitude. Perhaps it is expecting an input signal level very different than what this TV provides. What I see on the screen is a very washed-out image of "colorless bars," with very faint indications of rolling bars (or whatever).
After double- and triple-checking everything on and around that transformer, I can't find anything wrong apart from this simply being an unsuitable part. I think I will pull it out and go back to the original. If the windings on this transformer looked more like the original ones, I might try removing the 680-ohm resistors and substituting 1200-pf caps for its 1500-pf ones. But that might just be time wasted.
Phil Nelson