New Generator

The new generator was installed in my Quetzal. Now the problem is that the old exhaust outlet is a bit bigger than the old one. The old exhaust is 40mm, the new 50mm. The company that installs the generator suggests to reduce the diameter. Another variant would be to enlarge the fuselage passage, i.e. to replace it. Is there someone with experience 
Thank you for your messages, stay healthy. 
Heinz sv Quetzal, Sm 2000, 292, Whangarei NZ at the moment because of Corona unfortunately not on board but in Berlin 

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