It's going to be WAY bigger than 780 square inches. I'll bet he's describing more like 1500. This size model is out of my league....but my guess is it would take one of the 1.5 cubic inch [or so] model engines to be a good performer.
This size airframe will need X amount of prop disk and a piped DF engine's only going to tolerate so much prop before it refuses to stage.
I'll be interested how this all turns out, mostly because I'm shooting from the hip with this opinion and have no real world experience with this exact application.