Do actually expect a cylinderhead that's been in place for 30+ years to
just lift off?
It's stuck onto the head gasket and that's, in turn, stuck onto the
block. You need to pry it off.
It could also be that someone, in an attempt to avoid replacing the
cylinderhead gasket (again), glued everything together with Permatex as
he assembled it. One never knows what's been done.
Most mechanics, who once worked on old engines like this one, retired
long ago, some of them permanently. There's not a vast knowledge
resource base to tap so temper your expectations as to what's available
for your old car project. I'd expect your car is older than half this