The reason it's called an "Export Brace" is because it was originally made for the "T-5"; the German Export Mustang. German Transportation Dept. requirements stated that the suspensions for the T-5 must meet certain specs, so, it had to be extra strong under the hood (presumably for the Autobahn).
So, Shelby saw the part, and added it to the Shelby Mustangs.
And, yes, it is one piece. If you put it on, save your original two pieces, just in case you decide to go concours some day.
Paul.