Cylinder head nuts- 8mm 16.5 to19.5 ft.-lb. (2)
                          - 9mm 21 to 24 ft.-lb.   (4)
    the nuts maybe 14mm . but the studs are listed by their thread size.

Perhaps you should wait for the answer to your questions Before you proceed ? It is interesting to note that the  NKG sparkplug that needs to be torqued into your head has a spec of 18 to 20 ft/lbs. in an alum. head,  it seals the head against compression too.  if you had gone with that number(20) it would have had you very close.

I've learned the hard way many times ,I think the best thing is not to make the same one twice !

Torque above what's listed ,may not even be possible , you'll likely just be stretching the stud, and the torque will then return to it's normal level. If you waited too long between torqueing from 8? to 24 ft/lbs  ,( did you torque after returning from your trip? ) the copper washer may have air hardened . You may have to anneal it and torque again.

they shouldn't be installed hot, I just didn't know if had delayed too long. It may have helped if you spread a thin layer of RTV on both side of the copper washers as oil does tend to migrate between the copper and the casings.

I would not quench the washers , I think that would harden them , the opposite of you want to do.

Regarding annealing, I have always used the heat and air-cool method.  It seemed to work OK.  Then I got new copper gaskets from Copper Gaskets Unlimited.  They provided annealing instructions.  It seems the water quench is the way to go.  I have attached a jpeg of their annealing procedure.  Since CGU is in the copper gasket biz, I figure they probably have the inside scoop.

Regarding the application of sealant to the copper washers, I have been testing the cylinder studs to determine the best tightening method.  My cylinder base gasket failed.  When I disassembled the engine to replace the gasket, I noted that the cylinder head nuts did not seem all that tight. Those nuts were installed with silicone sealant on the copper washer (both sides).  So while its apart, I decided to do some tests.  

At the specified torque, silicone sealant applied to the washers reduces the stud stretch dramatically.  I have tried three different silicone sealants and the results are identical.  With sealant applied to the washers, stretch drops from .019" (with oil)  to .009" (with sealant). That is a bunch.  Note that the factory manual specifies oil.  If you think that you can rectify the problem by simply applying more torque, I would not advise it.  When you start taking the nuts past the maximum specified torque (24 ft-lbs), the washers start galling.  At 600 inch-lbs (50 ft-lbs), the stretch was only .017".  I quit there because that's the limit on the torque wrench I was using.