Thanks to everyone for all the good advice above, gave me some good diagnostic help.

Thankfully have got the motor going, sounds great running straight out the extractors without pipes. Hopefully take it for a blue slip in the next week.

Turns out I had 2 problems. First was the pushrod/rocker problem not allowing the valves to properly close, which I fixed with shims under the bridges (may revisit shorter custom length pushrods later) and then once that was done it would run only with the bypass wire, had to replace ignition switch too.

Its been one of those jobs.