Paul, thanks for confirming you DO need a nice strong signal to drive V7, I was unsure about that. And thanks for having yours opened up and taking measurements for me! A working test mule is the best mule!
In post #54 I said about V6 - "Pin 7 (tube side) to chassis ground - Horizontal gain pot min - 0K. Horizontal gain pot max - 12K."
I would think that would rule out the pot, but I'm desperate so I went and tried your "shorting out the pot" test out just now anyway. First I had to reconnect the gray wire coming from V6 pin 6 that I disconnected last night and had a little bit of an AHA! moment, as I had a bit of a tough time getting a good joint (dirty wire I reckon) and though maybe that joint was bad in the first place.
Powered on, same result. Powered off again. Pins 1 and 3 jumped, powered on again, same result. Reflowed all joints on the horizontal gain and horizontal position pots and checked the connections on the gray, purple and brown wires (gray from V6 pin 6, purple and brown to coming off the horizontal position pot) from end to end and everything looks good there too.
V6 still simply refuses to conduct. I'm out of ideas short of finding a nice tall building and gently heaving this thing off the top of it.