My '99 'Stang passes without cats. It has quite a few mods (including a Bassani O/R x-pipe) and a tune. I was told 99's and older are tested through the OBD port not the tailpipe. However, depending on the shop it could fail a visual. I remember years ago, people would hollow out their cats; nothing in them but they would pass the visual. IMHO, it's a crap shoot. Some shops will pass them with no cats, others won"t.