OK no dimensions tonight but I did manage to take some pictures.
Yes this is a 1978 SI by midway - B&W monitor with film over the tube.
First pick shows the back of the mirror. It's more of a silver tone and you can't see thru it very well (At least not at 8:00 PM at night in my garage

)

Mirror with the light on:

Monitor looking down on it:

Mirror and monitor with game on:

Picture of monitor as seen in mirror with game off and flash on camera:

moon glass and background:

View of game play from front:

Hope this helps.
I'll take more detailed pictures and take dimensions over the weekend.