your joking right?

your going to try to desighn a trainer around a 6 foot wing and an 8 lb engine and only put out 2 hp? My war bird weight 11 lb with a 6 foot wing and they are considered heavy, this is not even in the ball bark, it has a 1.5 lb engine putting out nearly 3 and though flies well need some runway.

Your best chance at a cheap engine is a small weed eater and even then the engine need t be highly mortified, lots of metal removal and balancing. I'm no saying it can't be done, just get a real trainer first , learn to fly then build a lead slead.