Your wing loading is probably going to come in at around 28 ounces per square inch at this point. It will be very interesting to see what this plane's glide ratio will look like. If the 61 FX doesn't seem to provide quite enough power, then you could opt for a 75 AX, which would fit the same bolt pattern yet offer more power. Larger wheels would also help accomodate a larger prop, and that may help put more air over the back control surfaces and offer more torque. You will definitely benefit from the use of the flaps. A large prop and lower "gear ratio" coupled with a stump-pulling engine is what gives a 3D plane the capability of flying below stall speeds. That, and the thicker airfoil with larger control surfaces, of course. In your case, I think you'll want tractor-like accelleration and enough muscle to to get that freight to its destination with adquate airspeed .

http://www.alaskawings.com/images/Carvn04.jpg

NorfolkSouthern