Hello!!
http://www.jettengineering.com/
In "actuality" the Aurora is designed around a Rear Exhaust engine...Of course that doesn't mean you can't put a side exhaust engine on the Aircraft with a little modification!!
My 45 kit is labeled as a Aurora45/Aurora45 S...The "S" denotes Side Exhaust...They sent along a little supplemental sheet for the Side Exhaust Engine Instillation...(I could make you a copy of the "supplemental sheet" if you need it)
For a Rear Exhaust application...One little "Fly in the Ointment" is how you plan to do the landing gear...If you intend to do a trike/retracts per the original design...A Rear Exhaust engine will require a "non standard" header which comes off the engine at approx a 45* Up/Left angle to clear the nose gear retract...(I actually think it's pretty common on the Old School Pattern Aircraft)...
So in a way...Using a side engine may be a tad bit easier if your going to do the Tricycle gear...A 4C engine would probably eliminate some of the nose gear interference issues also...
Just some food for thought...