You are having all the fun. They didn't have this kind of thing when I was a kid. Well yeah they did, it was the old PAA .049 powered cargo event. There were some great models designed for it. I think Model Aviation or one of the magazines had coverage of a recent lifting contest a few issues ago.

The resulting airplanes are just plain homely. It is a great technicial challenge though. As Bruce said the lift goodness from the big end plate on the bidplane has got to be a lot. Plus some structural difficulties are made much easier. Be sure and make something that can fly well in addition to carrying weight.

Be sure and post a photo of the final result.