Job's complete, eventually... Taking the IM off, fitting all the bits to the new IM, cleaning the valves, ports, and TB, and then fitting it all back together.... took me about 20 hours in total, maybe more!  It is a right horrible job to do, but it was very necessary.  Annoyingly, it hasn't cured my warm idle engine twitching, but the throttle response and acceleration have improved from what I can tell.  Never had it on a rolling road so have no stats to compare, but it definitely seems better