I have one of these still in the box, and two Magnum .91 4's ready for it,
http://www.nitroplanes.com/giscce310sc6.html
Also have the Hobby Hangar OV-10 Bronco, with the retract kit. Good candidate for the .91's...
http://www.hobbyhangar.com/test/acc.htm
Remember, two motors will generate more thrust that an equivalent size single...sooo, two .91 four strokes will pull like a OS 2.00 single and close to a Saito 2.20 four stroke...so size your plane accordingly.