Sorry to jump in on this thread, but since I am thinking of building a rotating monitor myself, I thought I would put in my 2 cents worth.
On my last 3 arcades, I used the black foam poster board, covered with plexi-glass.
This works real well for me, only problem I see is the mirror-like reflectivity in certain ambient light situations. I have not tried smoked plexi, maybe this would cure the problem, but the black behind the clear plexi is very close to a mirror.
The arcades I have done so far have fixed monitors, so making a bezel for a rotating one is going to be a challenge.
I will be following this thread.