Check the plastic & rubber lines going to the vapor canister. We had the same problem on someone's 92 GT back in high school auto shop (it also, coincidentally, had a leaking injector o-ring, but I spotted the vapor lines first). Those lines get cracked easily because of their location, but I think that's what you're smelling, if you're smelling gas around the air filter. Heck, the canister's right below it! One tube goes all the way back to the gas tank, another goes to the intake manifold. The canister itself could be cracked, too, so check everything out. Good luck.
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Capri306, Moderator, The Mustang Works Online
1979 Mercury Capri, 5.0L -- C4 -- 2.73
1987 Mustang LX Notch 
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