are you still thinking of coming back to Christchurch Craig
shame you're not down here with now as i'm sure there's f all wrong with it and we'd get it running in a couple of hours
sure a shame to give it away at that price. Don't give up
To me it sounds like timing for sure, I know you've had the dizzy out and dead timed it, try that again and take the front cover off and check the both cams timing as well, if it's back firing it appears it has everything it needs to run except timing is wrong

I have seen a bottom cam pulley buggered where it is keyed on to the crankshaft, that causes major timing issues as well.
cheers
Tim