If you use a 2 stroke, you may want to put the rudder servo up front and use a pushrod or a pull-pull system to keep the CG where it belongs. If you use the suggested plan of rear mounting the rudder servo, you will end up tail heavy and need to lead to nose. If you use an OS .70 4 stroke, it will balance perfectly with the tail mounted servo. If you have ever thought about going to 4 strokes, here's your chance! You won't regret it. The OS .70 is a perfect match for this plane. Add some down thrust to your engine mount to make it fly right.