I guess the only other thing to mention is that the opening that the servo drops into needs to have a gap all around the servo.

As to the question of 2 Vs 4 screw servo mounting orientation, it is best for either to be mounted so the long axis is in the direction of force. Why bother with expensive digital servos and not give them every mechanical advantage? While most trainers have the servo locations fixed, later models that may even be built by a modeler usually leave the mounting detail to the builder.