Well,
Finally got to the bottom of why the bobtail is misfiring.
A mixture of code reading, multimeter and probe testing confirmed #6 and 8 injectors are not happy. 6 is intermittant and 8 is not opening at all. Noid light confirmed wiring and connectors are fine.

So,
I've ordered a couple replacement injectors and a complete seal set.
My theory is that I perhaps upset crud in the system when I had the heads off. The overall engine condition aint that great inside, see worse, but I wanna live with it until I find a unit that I know will be way better if I'm gonna go engine replacement route.

Once the injector bits arrive I'm taking the rail off with injectors. Should I soak the injectors in a container of fuel? I'm assuming it doesn't matter if they don't go back in the same rail position? The replacement seals are listed as silicone not viton but literature I have read suggests smearing a little silicone grease on them to aid the sealing, a good idea using silicone??

Replacing injectors is gonna be new to me, so would appreciate suggestions, tips, advise etc?