I have an 82 as well. Our motors are underpowered to begin with and to use the A/C would tax it even more. I removed the whole unit and purchased the engine tin that completely covered up the gap. Id either not use it or remove it. The key to longevity to an air cooled motor is to have a completely sealed engine compartment. Make sure your engine to body seal is intact and that it fits snugly around the entire engine compartment. Basically you don't want to see any "ground"/"pavement" when your looking down on your engine.
A gentle foot and pure synthetic oil will help the life of your engine better than an air conditioning unit will.