Well it's certainly an ambitious project for sure. I can see how the weight is pretty much set even before you start.

A thought for you...... Since most of your weight is in the engine and drive train components it would seem to me that increasing the size of the shell a bit would not increase the weight by as much as it would up the wing area. Even a jump up to the high 70 inch to low 80 inch span would offer a big improvement in wing area if you stick with the fudged wing outline. Provided you think the power output will deal with perhaps a couple of extra pounds and with careful airframe work I would think it was possible.

Some possible avenues to lighten the weight but retain the strength. If the shells were made from light outer skins with a 1/4 inch foam core and an inner skin to simulate a honeycomb style laminate the skins could be made lighter for the same stiffness. I suspect that with care and if the foam inner cores could be heat formed before the layup then you could get away with about 1/2 to 2/3 the wieght of glass and resin that you'd need for a similarly stiff and strong shell. High stress areas could use wood or carbon fill to help spread the stresses out. Or even if you put the same weight of resin and cloth into the shells the double wall cored method would allow you to greatly reduce the inner structure neccessary to support the airframe. In effect all this would help you build in more air and less material for a lighter weight or an increase in size with minimal weight impact.

The Selig airfoil is basically already set up with "pre-deployed flaps" built in thanks to the high camber and severe trailing edge cusp. Adding flaps to that one would not really help with the lift but it would add a lot of drag. Probably not what you want. The 8036 would benifit from flaps. Fowler sounds good and at larger sizes I know it works better but at our model sizes it's hard to say what the airflow through that critical gap is really like. If the gap is "scale" it's likely it's too narrow to really blow the top of the flap. At that point you may as well just stick to simple flaps. Frankly I think you'd need a wind tunnel to design a proper fowler flap system for model sizes. Without such fine tuning I think it's doubtful that you'll get enough benifit to make up for the extra weight, not to mention complexity. If I had a choice I'd go for the reduction in weight and simplicity.

I suspect you'll also be running into much of the same problems with the drivetrain that the original Boeing team did. Vibration from drive train harmonics and all that. Best of luck with the project