Javven has the right idea
Javven has the right idea when he suggests a biplane. Although it would not have to be a biplane, but rather a plane with a short moment on the nose. Typically scale biplanes have short nose moment and you would actually put the extra weight to use instead of compensating for it. I have been bench running a 3250 for an Ultrasport 1000. (power to weight should match that of the previous lawnmower pic). I did have the typical transition problems with the stock carb, changed to a perry mega carb, and the problems went away ($35.00). As for being a boat anchor, big tigres are heavy, but they are designed and built for RC, to withstand a lot of punishment and run forever, not to edge the yard once a week. Mixing your own fuel is the way to go, as the big tigres like to drink quite a bit. Definately break the engine in with at least a gallon and follow the tuning instructions.