Why do you want to mount the servo aft? I built my per the directions using standard servos/batt and a royal .46. The plane balances per directions. I tried adding some tail weight to see what would happen and it just made the plane hard to fly inverted (kept wanting to climb) so I removed the weight and left the CG per plans. The magic is one fun plane to fly!! I wish I could get another as a backup but no one has them.

George