Ed,

Do you know, Radio Control Hall of Fame?

http://www.rchalloffame.org/

Look on right side of the page for:

First proportional?
Doig's Ulti Multi

This does show us the time line of the early period of proportional radio's, scroll down for:

Early Proportional Timeline

http://www.rchalloffame.org/Exhibits...t11/index.html

I also did some experiments with analog proportional.
Problems were, weight and temperature stability of servo position.
Digital was more easy for the scratch builder.
Important parts of the decoder were a little (transistor seize) semiconductor, thyristor BRY39 (digital) and not 2 heavy coils for each proportional channel (analog).

Cees