If it's from a 20A1 chassis, send me a PM (or go to
http://antiqueradio.org/contact.htm) and let's work out a deal.
If it's from another Admiral chassis, the back of the HV cage is 5” wide, with holes near the top 4-1/2” apart. The top part of the HV cover is 7-3/16 inches front to back. Apparently the HV covers aren't all interchangeable, just as the back covers aren't.
Regards,
Phil Nelson