Be sure to mark the plastic blower assembly before you take it out. I am not sure, but at least with the 300D blower it is easy to reinstall that casing with the new electic blower and get the thing turned. Seems the screws will still fit in there with it rotated a third turn. Then the defrost flap will open and jam into the blower fan. I has to go back with the same orientation as it went in with.
Like I said I haven't had the 300SD blower out yet, but have had an adventure with the 300D fan.