I have finally managed to remove the Aperture Plate from inside of the Trap. (Both seen here from the back). The aperture has an aspect ratio of 1.27:1 and has rounded corners. Also, this aperture plate is not meant to be filed, or interchanged. It is supposed to be factory cut and seldomly removed. I guess I will have to devise a way to interchange aperture plates...
Seen here from the front. The round hole in the Trap was a first one for me.
The Shutter Drive (still in the projector).
The sticky filth all over the Shutter Blade made it extremely hard to spin.