I whole heartedly agree with Bill. Use two servos. If you have a computer radio, there are very good reasons, in addition to less play in the linkage, such as ease of set up, if the servos are on separate channels and mixed together. With separate channels the top and low end can be matched easily. Now, as you are building a fun fly......consider mixing the throttle servos to the rudders......ABOVE 50% throttle for safety. Imagine knife edge and flat spins with differential thrust!!!
Good Luck,