the most awkward bolts are 2 of the inner ones on the inlet mani to head mate, i always left them off
or you can lift the head-mani as one (longer job)
but i did loads of head swaps in situ
3rd gear is usually when the ecu transfers to closed loop fueling on acceleration
you can check if its running too lean by monitoring the lambda voltage with a volt meter or freeware
https://micra.org.uk/threads/tost-the-official-spam-thread.53370/page-63#post-651217