The previous owner of my D5500 broke the little ears off of the front cover of my enlarger. It is now held on with a rubber band, kind of sad really! If anyone has one that they would like to part with or even a whole broken D5500 Dichro head, please let me know.
You can put two holes in the front cover and use thumb screws to hold it on. There are even dimples on the back of the plate where the holes should go. You will see on the head where two screws can be threaded. You will likely need a tap to start the threads. I have 4 front covers, and only one has the two ears still intact. Jandorf (available at hardware stroes in US) makes a plastic plug that fits perfectly in the existing holes in the head so there will be no light leak.