It is possible that an 87 300SDL could have a 10p15c compressor. If so I would guess it to be the only 126 using a 15c. The 15 portion of the nippondenso number refers to its displacement or capacity.
From the original description of the part it didn't sound like the proper part. It still doesn't due to the pulley difference and the lack of speed sensor installed.
Because of the way the Nippondensos are mounted you are pretty much stuck with using what came on the car. The 17c compressors have a different bolt pattern.
Bosch Master, ASE Master, L1
33 years MB technician