Great picks, zhandax.
At that mileage, I would suggest a compression test to determine if the head needs to be done. See my post on "1986 compression test results". Although the seals are a given. I always try the cheap thing first, but let the pro's give us the input.
For what I have read, the motor mount on the driver's side will be much easier to change with the air intake removed. I could not find the bracket you mention in any of the parts catalogs I have laying around.
From the picks I see the thin arm is the one that caused the hole in the substrate, does it excert more pressure?
Good work, please keep us posted.
1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car