I take it your adding one over the existing factory one
If it were me , i would pull the factory one first(5 minute job torx screws)
That way you could see were the coolant hoses route and if its an 2003 now is a good time to check your hoses and replace or wrap with plastic hose wrap - The 2003,s had a bad habit of rubbing in alot of places well at least on my F5,s - In 2004 -2005 they wrapped all those coolant hoses
Anyways i guess i call it piece of mind and like i stated , 5 minute job removing factory skid plate to take a look on were to drill - Scott