I've never read anything pertaining to re-torquing the head. The factory manual does not call for it. Also some gaskets are not supposed to be re-torqued, like the Fel-Pro Perma-Torque.

For what it is worth, some engines do require a re-torque, just not the 2.6.

As far as valves, every 10-15K is crucial.

Good Luck,
Michael