The first job I looked at was the boom servos; each boom has 1 elevator and 1 rudder servo. The cut-outs didn't perfectly suit any of the servos that I had so I tried a few different ones out to see what I wanted to use. In the end I have decided on Hitec HS-85MG for the rudders (as I had some spare) and will use Hitec HS-5085MG for the elevators. These seem quite small but previous experience flying a Wren 44 powered Savex L39 with Hitec minis on aileron and flaps makes me think that these will be fine.

The HS-85s fit pretty well into the rudder cut-outs; I have just added a strip of 1/8th ply at the bottom for neatness. The elevator servos were a little more tricky as there is not much depth for them. Also, one of the pieces of wood that the elevator servos should screw to was a little loose. I ran some cyano around the loose part and then made some 1/8th ply mounts which I glued over the top. This creates just enough stand-off for the HS-5085s to fit without sticking out of the other side of the boom.