Looking back at
the circuit I concocted I noticed that the adjustment for the line sync freq/position had a stupidly large amount of range. I just checked what I actually used. Instead of the single adjustment I included a 3 position switch selecting between 2 preset adjust pots and third pot with a knob.
The actual values set on the presets were 8.3k for 405 lines 47k for 240 lines and the knob adjustment pot was 100k just for messing about.
Looking on my Sony 9-90 on 405 lines none of the settings resulted in hooking of the top of the picture but the 9-90 was quite critical to display correct interlacing. I'm happy to report that the 9-90 worked correctly on the 405 line preset that I last adjusted 4 years ago.
Peter