Upon searching Ebay sites from around the world along with several EPC's, it seems the 3.92 was the shortest ratio available that fits into the 185mm W124-style differential housing.
It was found in several models in Europe between the late 80s and early 2000s, usually paired with smaller 2.0-2.6L engines and manual transmissions.
The differential housings have some differences, but the 3.92 ring gear and pinion part number is the same for the W201, W202, W124, W210, W209, R129, and possibly other chassis I am forgetting.

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