The "analog" proportional Citizenship radio were really just fast pulse proportional systems with analog servos. Which is why only three functions were controlled, though a fourth servo could be added to add the CAR function (coupled aileron rudder). There are several interesting circuits and concepts with the C-S AP sets, but the were not on the market very long before cheap digital systems took the segment.
Most analog systems were closer to reed sets, since they encoded information with a frequency shift and used a frequency discriminator to provide an analog signal to the servos. Limitations of bandwidth, and inter-modulation between control tones also pushed some analog systems into a time sharing scheme to add additional control functions.