If you have EI its not a good idea to pull plug leads off with the motor running, theres a high risk of spark energy feeding back and disrupting the EI tiny bits. If the plugs are removed and clipped to the motor so they can spark, thats OK, but the spark must be able to jump somewhere.
Allan makes very pertinent points about the barrels.
For the head joint to seal all must be flat, at a push I have lapped the head to the barrel with lapping compound and a figure of 8 motion. plug holes with blue tack firstt to keep grit out. Clean thoroughly before reassembly.
last time I blued the joint and found raised areas around the barrel threads, scraped then re blued, did this a couple of times till the blue took all over.
Also check the head around the bolt / stud mounting holes where the washers bear against the alloy, these areas can distort , usually bellied to wards hole, my head needed 3 of the spot faces truing up, worst one was the centre bolt mount, it was cockeyed.
The only good fix for this is a man with a mill, spot face washer lands back to true level taking off just enough to clean up.
All head fastener washers should be thick types, normal washers wont cut it.
Make sure head bolt holes are not nipped around the top due to distortion, get a drill that fits the undistorted end and use it to clear the nipped top area, if tight this can trick the torque wrench, all going slack after a couple of heat cycles.
Do retorque after a couple of heat cycles, yes it means disturbing the exhaust rockers, , but I find that at least one bolt/ stud will settle , usually more, centre and front last time I did it.