will a h80i with an asrock extreme 6 fit in a corsair 300r?
You will have to specify what socket you are using. There are Exteme boards for every socket. If you are talking about Z77 board, it should fit just fine.
It'll fit no problem.
I read that as: "Will it all fix?"
I am almost disappointed, as my expectations for a comical post were smashed under the weight of a legitimate question.
If you have a 120mm fan mount, you're good to go.