I have a Saito 100 glow on mine,and I honestly think it's the perfect motor for a Pig. I also honestly think 20CC gas is to big a motor for it. It's also my belief that below 20cc gas engines start getting prohibitively heavier in the power to weight ratio. Mine balances perfect with a Saito 100,and it tears up the sky

All that said,if I HAD to go gas,I would probably go with the DLE 20. I think it's the best bang for the buck,and the most power for it's weight. I have both a DLE 20,and 30. Both are very reliable.
Saito 100's and .91s ( a .91 is a good choice also) both go extremely reasonable here on the classifieds. Of course they might need new bearings,but they really aren't that hard to put in. I still love my glow planes

Hog bipes have kind of a cult following.they are "unique".
There are 4 or 5 pages of them here on Fubar hill,just scroll down to hog Bipes.
http://www.fubarhill.com/