Thanks for writing...!
Actually, the regular silicon flexi type work just fine.
Be sure to get the LARGE size one. It is important that the center pathway in the diverter is larger in diameter than th exhaust outlet. This way no backpressure, and no problems.
This is a good example of your application
http://www.jettengineering.com/hall/ms-f16.html
Be sure to use a bit of RTV silicone to help keep it in place. The tie wraps are required too.
If you want to go with Aluminum,
something like this.....
http://www.jettengineering.com/hall/pfister-f16.html
I think this is what Ken used...
http://www.macspro.com/accessories.asp I
THINK you need 9114 but NOT 100% sure. If you go this route measure the exhaust outlet OD first ..then refer to the chart on the website.
I hope this is helpful!
Bob