I re-read those Admiral servicing notes more carefully and discovered that the filter must installed inside the HV cage not under the chassis. I'm not sure if that affects the circuit or it's a safety issue, but I went ahead and moved it. I mounted a terminal strip to an existing hole and soldered in the components.
I also tweaked the capacitor value. I figure the ripple is a harmonic of 15,750 Hz. The closest to what I saw on the scope are 173 and 189 kHz. A little experimenting found that 189 kHz was correct so I went with about 5900 pF in parallel with the 120 uH inductor.
Unfortunately, while mucking around in the HV cage I managed to snap off a flyback lead. I melt back the wax a little and managed to solder it back on then coated it with corona dope. Seems to work fine after 10+ hours of playing.
Then on to cleaning out the tuner and going through the alignment procedure.
I found this date stamped inside the tuner.
Here's the IF response.
I spent a lot of time fighting with the focus coil, centering lever, ion trap magnet and yoke. It's not perfect, but certainly better than what I started with.
Here are a couple screenshots. You can see how the bottom right-corner bends up a little.
Another issue is an occasional hiss / crackle in the audio. it sounds just like a HV leak, but I can pull the HO tube and the hiss remains
