i installed mine without drilling any new holes in the roof by using the screws that hold up the visors. It looks really good, especially when the visors are up, you cant see the metal piece running between them. My pics aren't working right now, but you can see them in my cardomain site (see bottom of sig.)
If that doesn't help, you might be able to see what your working with by looking at some of the pics people have taken of installing the explorer overhead consols, they cut out the roof to expose the metal, that could give you an idea of what is behind yours. I'll see if i can't find the link.
EDIT: Here is the link to John Grigg's cardomain site, if you scroll down, you can see what is up there! http://www.cardomain.com/ride/296394/3
hope that helped!
2002 XLT Ext. Cab, Black, 4x2, 3.0 V6