It is not always necessary to remove the entire cowl top. I've had good luck with just removing the fenders, and cutting the cowl open there, patching, and weld it all back up!!
Here is a really nice article about rusted cowls in Mustangs. Mavericks suffer from the same poor design. Great pictures of a complete tear down and rebuild. http://www.mustangmonthly.com/projectbuild/mump_0103_mustang_cowl_repair/index.html
You can buy a kit to replace the "hats" as they are called. As far as a complete Mustang cowl - I know there are size differences between Mavericks and Mustangs so I don't think it would be a direct swap without doing some fabrication. Most repairs can be done to the rust holes and the original cowl can be saved. I like Joe's idea of cutting open the sides and welding them back in after the repair is made to the hat.
once the cowls are fixed can a screen or mesh be put on the underside of the grille part so that more $hi+ doesn't fall in there and cause us more problems. And does anyone have any pics of a side cut out job i am kinda wondering just exactly where these cuts should be made.