Product review (3 stars): The installation instructions that came with this hood are the worse I have ever seen
The installation instructions that came with this hood are the worse I have ever seen.  The hood itself was a good buy for the money but the install instructions were ambiguous and bore little pertinence to the actual hood.  I finally found this video on You Tube

https://www.youtube.com/watch?v=AjB42shF1Ts

Although it is for a different brand name  and a hood that is a four piece chimney, the bracketry is common and will be a lot more help for you.