Typically the doors aren't interchangeable between generations.
Looking at some pictures; however, they look damn close to the same door. Guess the only way to tell would be to take some picture of your '81 door (specifically, where it bolts to the car), and compare it to the guy's '86. Measure height and width at the base, where the door curves into the A-pillar, and at the top as well. Look at the height of the door striker as well. If they all line up, then it should fit like a glove.