Adam, had a look at the one on my 98 T Bird and can see your concern. If I was doing it I would take off the guard and line up the extension in place on a pile of rags or something that would not scratch. Perhaps use a contact glue to help hold in place. Then I would drill from the inside to the outer using the extension as the template.
Looks like small holes. I would clean the edges of the holes from the outside and bolt up. Maybe use some nail polish to seal the edges of the holes.
They look good.
cheers
Murray