You got to a good place. The back end slides off after those 3 screws come out. Then comes the motor which you deal with on it's own. You can pry it out by putting a flat head screw driver between the rubber around the back and the metal casing and twisting it. The first time it is removed can be rather hard because of dirt and rust in that area combined with the fact that it has been that way for 28 years.
The switch does not need to be removed to do motor work.
The switch does not need to be removed to do motor work.