All Mercedes-Benz wagons, since the start of production of the S123 in 1978 (as '79 models in most markets) are equipped with rear self-levelling suspension as standard.
The great looking chromed roof racks were optional up to the 1980 model year, they became standard later on (they were standard on all U.S. models).
My previous 1981 300TD came with the optional cargo roof holder. It was great, it attached directly to the chromed roof racks. Although it was a US$1,500 option at the time, not cheap!
I believe the W123s wagons in the U.S. came without rear headrests, unless the rear facing third seat was ordered.
The cargo cover and security net was available as an option in most markets, including the U.S.A. It was the same system as used in the W124 wagons.
I have never seen a S123 with crossbars. Only S124s. Although, they should have been available at the time.
The original M.B. roof accessories catalog is impressive, with about 35 different roof carrying systems for everything from bykes up to surfboards and everything in between.