The trans from the 300TE will work, provided it's not a 4 matic (4 wheel drive) version.
The part numbers of the transmissions are located on the drivers side trans rail, just above the pan.
Make sure you replace the front seal where the torque converter slips in...the rear seal is a bit more difficult but I would recommend replacing it as well, you can get a deep-well 30mm socket from Autozone, for around $7 to remove the rear yoke where the flex disc bolts to the rear of the trans.
The 2.6 and 3.0 share the same block/trans bolt pattern, as well as the 2.5 and 3.0 diesel block/trans bolt pattern.
Good luck on the swap, and Merry Christmas.
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'87 300E | 2.6 engine
Artic White - Navy blue interior, chrome rims, very clean and sharp!
91 300E
89 300E
The rest of my collection are just cars and trucks...no more "automobiles"...