I don't own one, but here is the factory service manual, courtesy of Dave S. of NJARC:
http://www.njarc.org/manuals/RCA_721TS_Service_Data.pdf
Note: 138 megabyte download.
Looks like the entire front panel comes off, along with the front glass. Look at the diagram & explanation in the installation instructions. Two wing nuts inside cabinet, two little screws under the panel front.
Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html