Thanks for the excellent guide. I would like to add a comment.
I did not remove the roof lining.
I used a Dremel as described with
a Right Angle Attachment.
View attachment 77645
first I split the casting i two parts as described.
Then I cut a slit in the length of the casting the first part of the split motor mount.
I used a screwdriver to widen the opening.
Then I spun around the part 180 degrees and cut a second slit on the other side.
Now it was easy to break in apart.
Repeat the process with the second part of the casting.
The I followed your description and mounted the the new motor mount.
View attachment 77647
It was no problem to do the job with removing the roof lining.
I am so happy with the New Motor Mount developed by Depronman