RE: Graupner Su-31 Engine choice ?
They claim an all up weight of 3.2Kg (7 lbs). If that's true then you'll want more engine than a 46LA... Depending upon the vertical performance you seek the Magnum 80 4 stroke may not be enough...
If I had to choose between the engines you listed I would go with Magnum. I really prefer 4 stroke glow engines in my aerobats...