If you take the gears out of a servo, it runs continuously until you turn it off. All you have to do (and you can do it with a switch) is reverse the polarity to make it go back to the original position. You can make stops, etc. You can even program (in better transmitters) a servo to do exactly what you want it to do (mostly). I have done this with sliding canopies on scale R/C aircraft.
You'd have to cut the gantry where you would want it to pivot and beef up the attachment points somewhat. I would just pick which side where the pivots should be and use that point(s), left side or right side. I have a Futaba TX with little dials: I can control the speed at which I deploy whatever is 'slaved' to that dial/channel. You can make it quite realistic.
It will take some original thinking, for sure! Have fun with it!
Allen