Each mounting point for the side cover is special, and changed during the run to keep the cover on the bike. My description should cover most P11As and all Rangers.
There are two tabs on the frame. one is on the top rail and one is on the rear downtube. A special bolt fits in that top tab and has a pin, about 1/8" diameter and a half inch long on the head of the bolt. The top of the side cover near the back has a hole about 3/8" diameter. A rubber grommet fits in the cover then slips onto the pin. The tab on the down tube lines up with another hole in the back of the side cover. this tab has a nut brazed to it. A thumb screw goes through the cover and into the nut, securing the back. The front of the cover has a forked tab that slides onto the outer stud that also holds outer bracket end of the left coil. A thumb nut and cupped washer hold this in place.
If you read through 'The P11 thread' I started here some years ago, you should find pictures.