It's good business to give a close estimate but always stipulate to customer unforeseen problems such as broken intake or manifold bolts and ect. I always tell my customers " It should take x amount of hrs with no snags but there is always possibility of some problem when breaking down and reassembly But as a start we will plan on x hrs."

As for labor on this particular job with no snags, i say 6 hrs if the wife lets me get a good nights rest the day before.

all this so accurate info made me want to create a database we could access and input an model and serial and job desription for job information... hmmm
now to add my $ 0.02USD
I would say it depends on what you mean by/include in "troubleshoot", but the rest is just about dead on (in my opinion) for a head job; "remove and replace the head gasket and associated parts including having a valve job done on the head".
how you and your customer got to the spot that it was determined that it was in need of a head job, that may not be as straightforward, imho.

$200 for machine shop work (cleaning, grinding, milling)
$125 for gaskets, antifreeze, oil

3 hrs to remove 3 hrs to install and 1 hr travel time

I would allow yourself any were from 4-7 hours but you should also consider has the head warped or even worse cracked? If cracked a new one will need to be sourced. If warped then you will need it re-skimming the time for this you will have to ask the specialist who takes on the job? Hope this helps

regards Suchy1977