The GEC RC410/R was described in detail in an 11-page article “A New Approach to H.F Communication Receiver Design” in GEC Journal 1967 Vol. 14 No.3, 1967. This covered both the receiver circuitry and the synthesizer, with block schematics but no full schematics. There were also some additional references in this post:
https://www.vintage-radio.net/forum/...2&postcount=11.
Cheers,