Kind of hard to get measurements whiles it's on the car.
But I got under there with the tape measure and got the following measurements.
Length = 29cm (11.6inches)
Width = 24 to 24.5cm ( 9.4 to 9.6inches)
It also seems my current design is.
3 Inch centre inlet
3 inch off centre outlet
All of the designs I could find on the Hooker Aero were either
3 inch off centre inlet with a 3 inch centre outlet.
or
3 inch centre inlet with 3 inch centre outlet.
Not sure what to do in that situation
Any advice would be great.
Otherwise I guess I can just take this to AES and they can hook me up with a custom made one.