The scale of the original drawing is aprox. 4' wide x 9' tall.
The opening in the wall is 4' wide x 7' tall. 
There are a couple options which I will present here.

this represents the original drawing proportioned at 4' wide x 9' tall.

this represents scaling of the proportions to 4' wide x 7' tall
I would round out the scrolls
more than is shown here.

this represents a 4' x 7' frame and keeping the proportions of the original design drawing. There would be a fancy twisted bar centered in the open space on each side of the design. 

option #1

option #2


example of twist