My Fun 51 had a Enya 45ss...which weighs about 15 ounces, probably several ounces lighter than your Magnum. It balanced about perfectly with the Enya. At one time I added an ounce or two in the tail to try to improve hovering, but that made it almost too unstable to land. So yes, you might benefit from moving at least one servo toward the tail to make up for the heavier engine.

Your 46LA would certainly fly the plane and would probably balance nicely with the wing mounted servos. I expect it would hover but I doubt it would pull out with much authority.

I did not notice any problem with slop in the control surfaces using the stock push rod setup.