Cooling Shroud

This is a very good question!

The exhaust side of the engine is the hottest and must be cooled first. The shroud (from Rotax) not only cools the cylinder head but also the cylinders and is why Rotax makes this statement in the installation manual. I imagine the time and money you spent building and designing your custom shroud would have easily bought the Rotax one. 

Rotax would not have made the specific statement in the installation manual ("On 2-cylinder-engines the air stream must be directed from the exhaust side towards the carburetor side with suitable ducting") if it wasn't important. 

Also, don't forget the following statement that's found below the ducting one - "Pusher propeller configurations should not be used with free air-cooled engines without consulting the engine manufacturer (in writing)".

Keeping your 447 properly cooled is very important! 

Sorry about your situation; thank you for posting the question and fly safe!

That makes sense.  For the record, in the LEAF catalog, the Rotax shroud is shown as "no longer available."