I think the origin of that plane was the RCM QuikStik. I was learning to fly with Pilot Jr Box Fly's in the early 70's and this plane was published in RCM. It was .20 sized to use an existing flat-bottomed wing you might have had lying around. The Box Fly wings fit perfectly and were available from World Engines, the importer of Pilot aircraft. I built more than one of these. The plane evolved into .40 size with ailerons, then .60 size and finally an .049 size. They were tough and fun. You should be able to get plans from RCM.