System BLUE / capability to handle external RF fields

[Bonzo]

Outside this area we absorb very strongly - more than 100dB/octave (done AFTER Pre-Amps)

Just a small remark on this:
If you write it in this manner the OP may expect several hundred dB suppression at the mentioned frequencies. However in practice you may be happy if the isolation is more than 100 dB in general out of the desired band.

And: filters behind pre-amps do not avoid intermodulation products generated by the pre-amps that fall in band.

I understood the receiver of Blue system will not much differ from the Red system. So the schematics is more or less available for further analysis.