Finally worked out what the problem was (although it wasnt me that worked it out - i was stumped!). Inside the distributor, the arm that moves back and forward (i think its called the interrupter lever) is 'rocking' very slightly but all over the place as the cam spins around.

This leads me to my next question. I am seriously considering converting to an electronic ignition as i need this car to be very reliable at the moment and ive had a few ignition issues in the past. On the IPD site there are two conversion kits (Crane and Perlux). Is installing one of these a good idea and if so which one is better? Or should i forget the conversion and just get a whole new distributor from somewhere (im in Sydney, Australia). Sorry again for all the questions.

Cheers,
Evan

p.s. hope everyone had a good christmas and new year.