To my knowledge most early to mid '80s W126 had Bendix calipers in the front and either ATE or Bendix in the rear.
There shoud be a stamp mark on the caliper, either ATE or Bendix. You have to take the wheel off to see it.
If that does not help, just go to your local MBZ dealeror call them with your VIN and ask them for the replacement part number.
81 300 SD grey/palomino 168K miles
84 190E 2.3 black/grey 64K miles (wrecked)
85 190E 2.3 maroon/palomino 92K miles
88 300E desert red/palomino 204k miles
(made to look like a '94-95)
92 400E desert taupe/creme beige 120K miles
(converted to 94-95 E420 looks)