The Banshee as a design was built around an Unmuffled, light Fox 35 and built with light balsa in the right areas. Any modern engine or engine with a muffler screws that all up. The plans to a new kit Banshee tell you to cut 1.5 inches off the nose, I'd go a little further but an OS 25 would probably fly the plane, if it was built out of light wood. SIG generally doesn't put that in the kits I get so an OS40 is usually what I end up with taking 2 inches off the nose and adding 3 inches behind the wing. You could also just glue the wing cutout back in, ifyou have it, and cut it out again 2 inches farther forward. But you'll probably still have to add weight somewhere.

Looks good with that long nose, hard to achieve from the kit form. Oh, and you'll need a good running Fox 35 too.