That is a 1939 HMV 1800. The mask is original. It just makes the tube look rectangular:
http://www.earlytelevision.org/hmv1800.html
By the way, the German E1, made in 1939, had a rectangular tube:
http://www.earlytelevision.org/e1.html
I don't think this guy is gutting the old sets, since a prewar set with original chassis is worth $6000 and up, compared to the $800 or so he is getting for these sets. I suspect that the guts were long ago lost.