i think the problem is the 'no plastic windows' thing. otherwise i would say the goldberg eaglet 50 flies greta on a 25 and can be built as a three channel. but it does have windows. seems odd to be looking for something that most manufacturers are stepping away from, that being the wooden box with wings. otherwise there are a few.

http://www2.towerhobbies.com/cgi-bin...?&I=LXJ567&P=0
http://www2.towerhobbies.com/cgi-bin...?&I=LXDJC0&P=0
http://www2.towerhobbies.com/cgi-bin...?&I=LXDJC4&P=0
http://www2.towerhobbies.com/cgi-bin...?&I=LXJ555&P=0

some of these have plastic windows some don't, but theres four ideas for ya.