Here, I just went back to the neighbors and took a pic of another one that I did for her. It is similar to yours. Now, don't make this any harder than it is. This was done using 2 deck screws. You don't need spacers doing it this way. Screw the screw in until you get the desired height. She hatches a lot of birds in these incubators I set up for her.
Thanks for the pictures.