if it`s really stubborn, then you may have to use the two nuts & mole-grips together!

Carefull, they might break! I had a cylinder where one of the studs broke, when I got some of the others out, it looked like there had been water seeping down along the stud, so they were rusted in the space furthest down the hole, thus making the stud diameter bigger furthest down.
I don't know if any heat or WD40 would help in that situation, but there are still two stuck, so I'm bathing them in WD40 for a month, then I'll try one with WD40 and a wrench and one with heat WD40 and a wrench.

When reinstalling, just turn them in handtight and then torque them when the head is installed.
There is torque data for the studs, but only torque the nuts on the studs, with the head installed. If you torque the studs alone, they will screw down in the hole with the part without thread (that is wider than the threaded part) and crack the cylinder around the stud holes. (Don't ask )
_________________
Poul
"If Life Gets Boring, Risk It!"
MC21SE, KISS box
MC21SP, HRC box, racing loom