Although this post was a year ago, I too have one of these that some wisecrack sold me. I tried the recommended .40 and it just waddled down the runway for about a mile. Stuck a .46 on it and it broke ground, this is when I found how poorly set up this plane was. Tough little sucker, did cartwheels down the entire length of the 800' runway without a scratch. In fact, that day, we purposely flew it to see how many cartwheels it could do before the top wing would come off.
Was looking through a copy of MA one day, cant' remember what issue, and saw two of these flying, actually in the air! I got the guy's e-mail through AMA and found out he and his buddy stuck on a Rossi .61 with a tuned pipe.
I stuck an enya .61 with a tuned pipe from one of my pattern ships on mine, adjusted the CG, and for once it flew with a little more confidence. Your comment about the top wing being upside down may explain why mine will fly level inverted but need 6 clicks up elevator in normal attitude.
Final note, throw away the landing gear and bolt on some sturdy aluminum gear into a solid block. The gear on mine kept moving which really made for quite a show when waddling down the runway.