I switched to a better scope and took some screenshots.
Here's the ripple riding on the horizontal deflection plate sawtooth
I was mistaken, there is about 12 VPP ripple on the 350 B++ rail.
I tried tacking in various filter caps near the deflection amps. Eventually, I got up to 120uF. That brought the ripple down to about 2 volts.
However, that had no impact on the display distortion. Very frustrating.