Rick,
Measure it.
My concert has mounting holes 12" center to center along the width of the head, and 8 1/2" from front to back.
22 1/2" wide by 4 3/4" high is the size of the chassis in the case, but since the concert head is "open" on the bottom you might want to add slightly to that for the height of the heads of the screws that protrude through the bottom.
The depth of the chassis - front to back, not counting the knobs in front or the heat sink in back is 9".