OK, I had the wrong circuit layout and diagram.
For reference, this layout is the one which matches the PCB and layout of Colin's monitor PCB.
http://www.zimmers.net/anonftp/pub/c...deo-layout.gif
Note the awkward error on that diagram - while the parts are shown, correctly, as they would look from above, the copper trace diagram is shown as it would look from below the board instead of, as it should be, looking through the PCB from above. The line output transformer is shown upper left, but the PCB pads it should be soldered into are shown upper right. The copper trace outline needs to be flipped over left / right.
Just to complicate matters further there are three distinct versions of the monitor circuit built on that PCB, namely
http://www.zimmers.net/anonftp/pub/c...01/video-1.gif
http://www.zimmers.net/anonftp/pub/c...01/video-2.gif
http://www.zimmers.net/anonftp/pub/c...01/video-3.gif
It would take a bit more investigation to work out exactly which one corresponds to Colin's but luckily his tweak to R20 (which is the 'vertical height' control in all three versions) seems to have sorted it out for the time being.