Here's a better photo showing the tail boom linkage - basically a pair of printed gears.
This design has fewer parts than a conventional linkage, less things to break so hopefully more reliable.
There's a 2:1 gearing ratio between the servo and the tail boom. The servo moves +/- 60 degrees which seemed excessive so I traded motion for torque.
The gears really need to be printed in nylon but for the first prototype PLA is good enough.
There's no slop in the linkage and the tail boom rotates smoothly, so that's a promising start.