I believe that the 1977-1981 (W123) chassis had a slide on shock absorber and the 1982-1985 (W123) had a bolt on shock. Both of which are changable. You basically have to remove the 17mm nuts that retain the shocks to the car. Once you have removed the bumper you can determine which style you need to get.

__________________
1994 E500 (MY SUNDAY DRIVER)
1993 190E SPORTLINE LE W/ M104 SWAP
1997 C230
2002 ML320
2000 BMW 528I (WIFEY'S CAR)

"Excuses are crutches for the unfounded."