Back in the late 70's and early 80's the Kraft and Futaba radios came with a plastic servo tray as well as a plastic tub used to mount a servo on it's side. Installation of the aileron servo such as you see in the Citabria was quite common at that time.

This is just a case of a very good and very popular kit staying on the market so long that it's not up to date any longer.

Bob Cox