Use the Explorer gasket set. The Mustang & Explorer have the same spacing and bolt pattern, however the Explorer is a better match for the port size on the manifold.
J, you beat me to it by minutes. All I can add is IF he gets a set, the middle of the manifold gasket is totally different from Stock to Explorer. (Talk about vac. leaks!) So if it is a stock size port to the heads, the Explorer set is the best way to get it all. I think the 97 Explorer Fel-pro set I have ready to go might have a metal core gasket on the head side even. I'd have to take a magnet up to the storage area to see if it is steel (and a caliper for port size), but it is not like the standard paper ones. The gaskets from Mr. Gasket and standard "performance" ones are meant to be hung in the showroom and bend without getting hurt. These are not that type of deal.
I checked the Fel Pro MS93334 intake gasket set I have. The bad news is the port size is just a little narrow for the tmoss ported Explorer intake or the extra ported E7 heads I have. 1.107 wide by 1.954 tall is the port size on the gaskets.
The good news is they have a steel core and feel graphite coated. They would be excellent stock size replacements. Check the catalog for which upper this is for.