Dart373, agreed. The Magnum 91 4 stroke is a great motor for this plane, and I recommend them to anybody wanting a 4-stroke that is on a budget.

If you already have a Saito 82, I'd agree wtih tukkus and go with it for sure. You mentioned this will be a "3d trainer".. you really WANT the extra power when learning 3D since it gives you extra insurance to pull out of manuevers that don't go well (like hovering). If you have to worry about pull, you will be less likely to push the envelope and learn new maneuvers. I say this from experience, as the Twist has been my 3D trainer... even though I'm still learning how to hover/torque roll, I feel comfortable trying it at low altitude because I know my motor will pull me out and away since I'm already hanging the prop at less than half throttle.

I built my Twist and assisted a buddy with building his... and tripp3d is right, they tend to be tail-heavy. With the big 91 up front and the battery/receiver in the logical locations in the fuse, the balance is within specs (albeit towards the front-most CG setting). Moving the pack behind the throttle servo puts the CG at the rear of the recommended range, which is where I like it. Certainly a smaller or lighter motor would result in a tail-heavy situation, but some folks have reported that the plane flies well even with a CG rear of the recommended range (in the 6+ inches from TE area) but I'm not brave enough to try it yet.