I think we are as far as we can go with only DCV measurements
Problem could only be a low value coupling capacitor e.g. C126 0.25uF 400V, C127 40uF 150V, C128 0.1uF 200V, C230 0.1uF 200V that you need to look at the signals with a scope, or test each part.
Paul Moir can you can look (with a scope) at the output of the sweep oscillator, for amplitude so we can know if it's weak here or not. Maybe V5A cathode or V6B plate. You might be able to measure it with a RMS multimeter (using an extra coupling cap to get rid of DC) like at C126 or V6A grid.
There's a chance there is nothing wrong with the H-amp and H-deflection or sweep oscillator. Instead, it could be the blanking malfunctioning. The CRT-beam being enabled for too short a portion of the sweep ramp. It's sweeping full H width but beam current only on for the inch, so it looks like a squished display, only a snippet is lit. Just a possibility.
V5B the grid bias is formed by space-charge and a very high impedance node with 22MEG resistor R142, so measuring with a 10MEG resistance multimeter there, the value will be thrown off. I think V5B is pulsed off? only for the retrace (blanked) portion of the inverted sawtooth it sees. So I would also check:
C116 100pF, C124 0.02uF 1,600V, R142 22MEG.
There might be a way to disable blanking, lift a leg on HV cap C124 or R144 etc and see what the screen looks like.