Question:

Are the rear brake calipers of the early 80's W126 compatible with the W123? I might want to grab a pair of rear w126 calipers

Looking in the pelican parts catalogue I see that the rear right, ATE is the exact same part number for the SD and 300D.. Both '83's.

Soooo, I should be more or less good, as long as the calipers for the SD are still in place.