A couple years ago I would've considered this an odd question, but after seeing (and hearing) how well my Chevy truck and Suburban manifold's seal without any gasket wahtsoever between the manifold and head, I'd be awfully tempted to try to go without one on my Mustang. If your manifold is flat, or newly resurfaced and the sealing surface on your head is nice and clean it should work. After all, new cars equipped with cast-iron manifolds haven't had gaskets for years, so why not try it? If you do try it, make very sure you don't use sealant of any kind and let us all know whether or not it works!