Not sure if this applies but I just changed two motors in the last two months. One in a 91 300E and the other in a 91 300TE. I purchased the motors from ******** AZ (
www.***************) part number 000 830 82 08 (non pollen filter). They came with the alternate mount. Both cars had the motor and mount pictured for the pollen filter cars on the ******** website. I had to remove the old mount from the cars and put in the new one. It was a simple process with three screws holding in the lower mount. There was another bracket on the cover that I had to remove. It was riveted in place and required drilling the rivet heads. The wires and terminal ends on the new motors were not secured so I tied them to the motor mount with plastic tie wraps.
I wasn't too impressed with the quality of the motor and squirrel cage fans, but they work and are a lot less expensive than the alternative.
Last fall I put a new blower motor in the 91 suburban for $46, but the 91 MB climate control system is much, much better than the suburban.