"Re-torquing of a cast-iron head should be done when it is hot.
Re-torquing of an aluminum head should be done when it is cold."
I just bought an aluminum stock-type head, and was instructed by the
manufacturer to torque it up the first time, set the valves cold, run
the engine to hot, retorque, then let it sit 'til cold, and reset the
valves. Go figure...
Have noticed on my Alfa that the iron exhaust manifolds need to be
retorqued to the aluminum head at least once after they are
reinstalled and the engine run--that old Differential Coefficient of
'84 Alfa Romeo GTV-6