Don't get carried away with all the Einstein launch the space shuttle theories. Regardless of the engine size any standard size servo from any manufacturer will work just fine. As for the distance from servo to motor is concerned, you would be well advised not to place the throttle servo in the vicinity of any of the engine electronics. This will limit the possibility of any interference. And yes, you can get interference with 2.4 systems and electronic or magneto ignitions. Whenever possible always ensure that the linkage does not bind in any way prior to being hooked up to the servo. A tight linkage will result in poor throttle transition. try to avoid "bell crank" linkages as well, they're a pain in the butt! Good Luck!

Loopman