it was my site you linked to, Mercedes-Benz turbo

but i do not think there is a straight swap, althou i havent tried myself...
have another guy here in sweden that are going to try and transplant the innards of a 3.07 w124 differential into his genII w126 diff, i can get you a picture of a genII w126 differential and a w201 differential (the w201 apperantly quite alike the w124)
but changing the innards of a differential is a heck of a job...

>> W126 rear diff swap << - Mercedes-Benz Forum

one perhaps better option you have is getting a gen1 w126 differential with the proper gearing and swaping out the entire subframe... or getting a w126 genII diesel differential, will swap straight away and give you a ratio of 2.88.... if you can find one of those...

(i might be stepping out on a limp here, but perhaps changing the innards of a 3.07 w123 differential is a possibility... instead of a w124)

best regards
/swampmonkey...

( a 380SE gen1 w126 has 197bhp and runs a 2.47 rearend, not to far from your powernumbers, if you are not looking for fast acceleration but good highwaycruicing, you could change the differential to a 2.47 genII, a diff from any v8, althou you would have to change the flange/yoke, and that is a heck of a job...)