This was a very neat project. The mechanics of the table top are very simple. I just used a but joint and wood screws covered with pegs to hold it together. For the most part no one has a hard time figuring out how to make the table top but some were struggling with finding the other components.
You can find similar diffusers in most flat screen screens. Now using the overhead diffuser is interesting because of the effect of its magnification but any diffuser would work. As for the clock. If you don't have a big broken clock around I would hit a store like pier one and but the cheapest big wall clock you can find. Go head and have it tell the real time otherwise pull the batteries out of it and solder a 9v power cap to the two end terminals and have a clock that runs fast.