[Vwdiesel] Head gasket problems

[Craig O.]

Questions to all experienced VW mechanics out there ---
  I just removed the head off of my 81 PU because of a blown head gasket 
and I had some difficulty with a few things.
I broke off a bolt in the left side upper radiator hose housing, and in 
addition while I was removing the thermostat housing (in order to drain 
the coolant) I also broke off a bolt.  In both cases there is enough of 
the bolt remaining to possibly get a hold with vice grips.  Is there a 
tip to loosening it prior to trying to turn with vice grips (IE - 
heating etc)?

AND -- many of the head bolt holes are filled with rust and oil sludge.  
Should I use a thread chaser to clean out the holes?  If so, what is the 
thread pitch on the 12mm head bolts?

Final question - should I remove the carbon deposits from the pistons, 
or just leave well enough alone?

Craig