about the extra wieght of the engine.

Look around at other thread about the plane. If people are using a certain engine, look at the weight of that engine and then see what they had to do to balance it. If they had to add tail weight when they were using an engine that was lighter then the magnum, then Dont get the magnum. If they had to add nose weight, check how much and then compare that to the weight of the magnum.

Overall, you want to add as little weight as possible to a plane.

If a plane is notorious for needing nose weight, then people can get away with a much larger engine then spec and have a wonderful powerhouse of a plane. If the plane is notorious for needing tail weight, then adding a larger motor will just make the problem worse. There is not point in adding a larger motor if you have to add more weight to the plane to get it to balance.