I know it's a bit late but I used NGK's in the Range Rover except for a time when I had a go on Bosch Super 4's which were alright. Dizzy caps - I preferred the black caps and always, always a genuine Lucas rotor arm. The misfire mentioned could...

FWIW there's a couple of things that might be worth checking. Are you sure the dizzy pick up is working, is the air gap correct? If the pick up isn't working, the ignition amplifier won't switch. Setting the air gap for the reluctor is easy as is...