So, after not finding anything externally, we pulled the motor :-(
Upon inspecting the rings we found they were indeed cut a bit to big, not drastically. We replaced them and cut them over correctly and have put the engine back in last night and stared her up this morning.
Still, on intial cold start up it will not idle by itself, but after a while it definitely got to idle unassisted a lot quicker than before.
Still doesn't sound like I've fixed the problem :-(
My next step is thinking of flying in my tuner
I don't know what else to do
Mechanic thinks it could be tuning related