Here we use the same aluminum foil, to cover the phototransistor. Make a small hole with a sewing needle or something so that there is a hole about 0.3 mm. Now the phototransistor registers only a small part of the film perforation.

 

Screw M3 x 19mm and spring from a ballpoint pen, used for height adjustment, plug in screw from top then wood on screw below.

 

This is the lower bracket, for the part that holds the phototransistors. It is an M3 nut that is glued with Super epoxy or similar 2 component glue and then pressed

Try with a film strip that the film runs easily and smoothly, if not file the lower part do not file too much so it is loose in height. Also try with the white starting strip at the beginning of the film may be slightly thicker. When you are happy, take a coarse sandpaper and polish on the film web so it becomes a little smoother.

 

Normally, such parts are made of metal, but we solve this with thin aluminum foil as used in the kitchen. Apply some glue and then glue on the aluminum foil, cut off excess foil with a sharp knife. The plastic layer on the film will run over the aluminum foil, the emulsion on the film then ends up closest to the camera.