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Cork composite gaskets have always been a type that compresses a lot. On the aircraft engines, most valve covers are secured with straight slot screws. The Lycoming screws have a permanent star lock washer swaged on. The whole screw gets replaced at overhaul so they hold up that long anyway. A person just snugs them up at each hundred hour inspection or sooner if we see one loose. Stock OEM gaskets are cork composite and usually last till the 300 hour valve inspection comes due. A screw driver applies just the right amount of torque. It's generally just snugged up after full contact. Maybe 15 to 20 inch/lbs. 30 inch/lbs shouldn't hurt anything on a new gasket but in may be too much on an old gasket. They don't compress as much as they break in. Some folks grease them but the oil will get to them pretty quick so I just put them on dry.
They last better on the old Fords because they are thicker so they compress more evenly and some have tabs that keep them in place.