Eric,
Aha! You have a problem in the timing of when the sync circuit starts the horizontal line sweep. It is locking up the horizontal oscillator halway along the sawtooth instead at the beginning of it, or if you wish, half of 63 uSec early or late to the video signal. What you are seeing is the horizontal blanking interval. If you adjust the vertical hold so that the vertical interval also appears on the screen you will have what the industry calls a 'Cross Pulse monitor'.
I have an idea. Since the damper tube starts to conduct in this region of the sawtooth I wonder if a pulse from start of damper conduction is somehow appearing on the plate of the sync detector or the H. oscillator tube. Might be from an open bypass capacitor?
I'll have a look in my RCA red pic-to-guides and see what Meagher has to say.
In answer to your question, the H. frequency is spot on, it is the phasing that is way off.
Rob