that wont get rid of the ripple in the metal though... eaither way, its going to be a PAIN in the ***. your best bet (imo) would be to tack on a sheetmetal panel to the bottom side of the hole (try and flex it up a bit) and fill it with kittyhair until its smooth.
but still, that metal is rippled to hell... looks like its more than 1\2" ripple in more than once place //content.invisioncic.com/y282845/emoticons/uhoh.gif.c07307dd22ee7e63e22fc8e9c614d1fd.gif
and i know from expierence... a garage collapsed on our 1965.5 mustang, and we had to cut a 15"x30" section out of the roof, and weld a new metal piece in, brace it underneath, and fill it with kittyhair.
its alot harder than i thought itd be.