Preliminary schematic for the IF and audio sections have been published:
http://www.earlytelevision.org/rca_color_prototype.html
In doing the IF circuits I compared them to the Sams folder for the 1952 RCA 21T176. The prototype set is almost identical, even the use of a choke in the filament line to isolate some of the IF stages. This indicates to me that the prototype was most likely made by RCA.
http://www.earlytelevision.org/image...Sams-157-8.pdf