To make sure all of the servos have the exact amount of throw for each engine, you may want to consider the Futaba Servo Synchronizer. Here's the stock number and suggested retail price:

FUTM4155 MSA10 SX SYNCHRONIZER $79.99

Here are the features:

It Couples up to Four Servos and electronically balances them to start and stop simultaneously for strong, smooth operation of even the largest control surfaces; plugs into a single rx channel.
You can adjust the end points and servo travel for each servo.
It also features reversing, so your servos can be mounted in the most efficient configuration possible.
These 4 servos can be powered separately from receiver.

You can purchase this through any hobby retailer who sells Futaba R/C systems and accessories.