Wilinfla,
I built one of these this summer and converted it to a tail dragger. I used a Saito 65 for power,more than enough. If I tried to fly with more than 1/2 throttle, it wanted to go left and up. That was with washers behind the motor mount to offset this. I think your Magnum 80 might be overkill. This is a light plane ; t doesn't need much power. With the Saito I didn't have to add any weight, just moved the battery up under the fuel tank.
Sam