Being that year or age, I would suspect the clasps will be rusty. You may get lucky and able to unscrew them, or you may break them. If you are wanting to sell the 'milk cartons' (as they are referred to due to being enclosed and plastic), you can look at taking a grinder the head and taking that off. Then the buyer of the cartons will have to figure out how to get the mounting off.
But so what. No one really keeps them anyway, or at least the wheelers I know. Even on the new JKs, they cut the out tubs off the front bumper making it like a stubby and the rear, they cut the bottom of the tub off to keep debri from damaging the lower body panels. Same for the large wheel flares.
To each their own.