Well it's a good thing that you went for the two day priority mail!Throttle servo thoughts tonight and I run into this mystery box. Unopened from 3 years ago, turns out these were for a science project for my son. We used regular servos on that project and I forgot about these. 2 are continuous rotation and the other is a boat anchor.
I often have to put a jog in the throttle rod to get around the tank. Your solution looks good.