We recently got this set, and were told that it was a Teletone:
http://www.earlytelevision.org/teletone_porthole.html
However, I can't find any Teletone like it in Riders.
The chassis is very much like the 621. I did find a few sets that used a similar chassis in Riders vol 3 and 4, but nothing that had a cabinet like this one.
Any ideas?