If it has 6SH7's then it must be an early chassis, I've heard of Hallicrafters using those Octal tubes but have never run across one.
Here's the schematic for the 6SH7 model.
http://www.earlytelevision.org/pdf/h...-rider-tv1.pdf
The CRT mask is just a big rubber thing that holds the CRT in the front of the cabinet, I don't like the fact that the CRT's in these sets are held in by just the base of the tube and the mask.