Help me with a cyl-head gasket mystery

Vaestertorp said
Fair enough. I´ll go for special washers and keep my fingers crossed. Thanks a million!

A followup however - since I already drilled my gasket and now must buy a new one: available here are FelPro or Corteco. Any opinions?

I would use a new gasket. You should be able to measure the bolts and the hole depth to see if bottoming out is the problem.