David,

There are some remarkable facts to show when I read your post.

On the advertisement you see a “modern” radio it was of the period I did fly "bang bang" and copied also parts of that set,(the modulator).
On picture 1 you see the set Gustav Sämann did use in 1960.

In Europe “reeds” weren’t often used. (Stegmaier is the only one I know)
An Electronic low frequent filter with relais was used for each channel (Schumacher filters, also a pilot), and normally two channels for a servo..
I think a good point were the multichannel “sticks” of Graupner of they early period, Orbit did use a two channel switch for each servo so you did have to be a piano player.
Electronic tricks were used to combine functions.
Picture 2 (RFJ) Gustav Sämann Dübendorf (Switserland) 1960 World Camps.

Cees