Maybe, depends on how the clutch bell and drive pulley mounts to the motor, if it's just a square bolt pattern and the housing isn't fitted around the motor odd then it should be able to just be turned 90°.
Quite some time ago I read about a Golden Eagle kit mounted in frame to a Micargi Bronco stretch cruiser chopper. Looking at a side view picture of the bicycle with the rear wheel on the left and the front wheel on the right, the main mounting strap (the one that bolts to the rear axle) was almost horizontal maybe at the 3:30 or 4:00 o'clock position with a Tanaka two-stroke engine fitted in the portion of the frame behind the seat tube. Judging by the picture the bike looked pretty good and seemed like the performance was satisfactory.