Sounds like you are on it like a chicken on a June bug, are you sure your name isn't Ed China ?
( BTW, that is one CRUDDY looking engine, never felt any love .... )

Do these have two cats for each bank? ----- YES
Fuel pressure on prime and idling is 54psi, at 3000rpm was 55psi, leakdown to 42 psi 30 mins after switch off...Are these normal figures? ---- YES
What is the difference between 'K' and 'G' leads? ----- ????? ( maybe H I J )
Compression on cylinder 6 is 200psi? ---- I would think that is quite high, 14:1 compression ?
Also,
a leakdown test on cylinder 6 showed 5% loss ---- don't know, probably acceptable