Those old clutch head screws are very difficult to remove when rusted. I found it easiest to take a dremel cutting disc & cut a slot deep into the head/ insert a large screwdriver give it a couple of whacks with a hammer/ then they twist right out.
Putting a little ATF on em never hurts either.
Of course, this method is only for those that are planning to replace the clutch screws, like I am.
