Here's a pic of where to find the stamping, bottom LH corner of housing as you look from the back. Took a bit of cleaning to see, but this one is clearly 2.88:

http://home.comcast.net/~dehlta/images/diff6.JPG

the W126 diff is slightly wider, measured from the faces where the half-axles fit, O/W the housing looks the same. The end result is that the spacer rings for a W123 have to be thinner, I believe that is the direction we had to go after stuffing a 126 diff into my 300TD. THe camber was out and tire wear set in before I figured it out. After the right spacers were installed it is OK, in fact right on, and I still drive the car with no unusual tire wear (after replacing 2 rear tires :mad: )
Here's a Ratio list I made up:

R107
380SL,SLC RATIO 1:2.47

380SL,SLC,560SL RATIO 1:2.47 ABS

450SL,SLC RATIO 1:2.65

450SL,SLC RATIO 1:3.06

W116
280S,SE RATIO 1:3.69

300SD RATIO 1:3.07

450SE.SEL RATIO 1:3.06

450SE.SEL RATIO 1:2.65

W123
230,240D RATIO 1:3.69

280E RATIO 1:3.58

300D RATIO 1:3.46

300DT 85 RATIO 1:2.88

300DT TO 84 RATIO 1:3.07

W126
300SD 85 RATIO 1:2.88 ABS

300SD TO 85 RATIO 1:3.07

300SDL RATIO 1:2.88 ABS

300SE,SEL RATIO 1:3.46

380,500 RATIO 1:2.47

380,500,560SEL RATIO 1:2.47 ABS

420SEL RATIO 1:2.47

W124
260E RATIO 1:3.27

300D 1987 RATIO 1:2.65

300E RATIO 1:3.07

Well, decided it won't go in this winter and I'll find another one by next summer so...., this one's gonna go.

Anyone interested, email me. Was hot-tanked, cover removed, everything checked, nice and tight. Comes with a flex-disk I couldn't get off at the yard (and don't feel like taking off now), cover was separately cleaned then re-painted while off. Installed with Ultra-black sealer.

Here's pics

http://home.comcast.net/~tomj/images/diff1b.JPG

http://home.comcast.net/~tomj/images/diff9.JPG

http://home.comcast.net/~tomj/images/diff3.JPG

http://home.comcast.net/~tomj/images/diff4.JPG

http://home.comcast.net/~tomj/images/diff10.JPG

Will also post in the Parts for sale forum as the more appropriate place to sell something.