Widen Chimney Breast from 50" to 54"

Folks,

I'm looking to buy a new fireplace and am considering widening the chimney breast by 2" each side to fit the standard 54" firelpaces.
You can get 48" but choice of fireplace is drastically reduced.
I'm thinking of simply fixing 2"x 1" battens and plasterboard each side to widen to 54 inches.
Is there anything else I should be thinking about ie. insulation etc?

Thanks in advance,

Bren.