For betula: Thank you for the information you have provided and for the various photos. I am able to view the speaker picture. When I was looking for the 638/645 schematic, I ended up purchasing it from justradios.com
However, your chassis may be different and thus these schematics may be no use to you. If you want a copy, let me know.
I, like you do not know what the RCC Supplement is so I will look forward to Jean’s response as well.