The Schematic Bank has a one-page sheet from Beitman. It has a small schematic and layout photo and the alignment instructions.
http://techpreservation.dyndns.org/schematics/58/58_Admiral_5RP42_11.djvu
You'll need the DjVu viewer plug-in. If you don't have it, you can go to the Schematic Bank's front page and use one of the links from there.
http://techpreservation.dyndns.org/schematics/
If you need something more detailed, Sams Photofacts has the schematic in set 387, folder 6.
:Hello all, just aquired this Admiral radio/phono combo. Schematic isn't listed here. Any thoughts on where I might find it. Thanks in advance,Tom