Chimney Cap options / Flex Liner in Brick Chimney

[jjs777_fzr]

Hi folks - I just ordered on friday a stove insert for my parents house - along with the staniless 6" flex liner.

The fireplace chimney is the one located at the middle-top of the roof.
The brick is solid on top and two of the sides - leaving two of the sides open for venting.
My question is with regard to what would you do to finish the flex liner / chimney cap ?
I was thinking about NOT cutting the chimney top and NOT installing the flex liner cap and instead just using the adapter plate from the flex kit and securing it as is to the chimney where it opens horizontally. Hard to describe in words but I'm sure you follow if yoy look at the chimney in the picture.
(The other chimney is similarly designed and serves the oil fired burner).

I am not afraid of modifying the existing chimney based on any advice - I'd just hop up there with my circular saw sporting a nice diamond blade and go to work. But I kinda like the look of both chimneys appearing similar.

 

[begreen]

It looks close. The opening appears to be only 2 bricks high or about 6-7". I would plan on carefully removing the current top cap at least to get the liner installed.

I'm thinking the flex cap plate could be attached upside down for a flush fit, then siliconed in place, then the chimney cap replaced. But maybe someone else has a better plan?

What material is the current chimney cap made from?

 

[mellow]

My take is you would have to cut that brick cap off to get the liner down, depending if you have terra cotta or not I would just use a top cap like this one:

You could then put the brick cap back on, hopefully with only two vents it would draft OK.

Bottom up cleaning would be pretty much the only way you could clean the liner if you reuse the brick cap.