OK, I have fine tuned the parts a bit. The actual prop would have about 9 slices for the sensor and I think, each one is about 1.5mm thick. However, if I were to follow this, the size of the sensor would be still be 13.5mm long. Give the wastage of about 0.5mm (blade thickness) we could be looking approxaimately at a 13.0mm by 1.1mm square hole from the toy, which is close enough.
If only I did not lose this part along with the stickers.
Anyway, I decided to redo them using 1.5mm acrylics and have them laser-cut. There will be nine pieces and an extra little strip for the 8 LEDs. I saw this on some of the actual props and decided to add them onto the frame. Hopefully, the laser-cutting guys can accomodate this design. The blank square on the bottom right is a bit wasteful but I have yet to find anything else to put into. I will try to build the kit following Gerry's manual and see if there are other things I can use for the blank area.