Here is a link to the Mustang Club of America's listing of the clubs in PA. I know for me the closest is the Valley Forge Mustang Club, which meets in Paoli (suburban Philly) once a month. I attended a meeting at the end of last summer. Everyone there was very nice. The local clubs are geared more towards shows & families than modding/racing, but are still good resources. As far as I know, all the local clubs require an MCA membership to be a member of their club as well, but I believe they all welcome guests year-round. Hopefully this helps.
http://www.mustang.org/regional_clubs.cfm?state=PA
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Proud Owner of an 05 GT
-Legend Lime Metallic, Black Leather, 5 speed, IUP, Machined Aluminum Rims, Active Anti-Theft
Mods: Flowmaster Axlebacks, Black 8-inch Shorty Antenna, K&N Drop-in Filter, Various MGW Interior Parts, Ford Racing Strut Tower Brace, Midwest Mirror Inserts, WebElectric Sequentials, 20% Tint, 18" American Racing Shelby Torq-Thrust M's & Nitto 555's, MGW Short-Throw Shifter
I'm a member of The Valley Forge club. As stated above, yes the club focuses on shows, cruise nights, parades and road trips, not much racing or performance modifications. When I joined in 1996, the club was 80% 60's cars but now is 80% 87-2007 cars. Also, you do have to join the MCA to join the VFMC. I'm still a member and I still enjoy those guys / girls.
What mustang clubs are in PA? 
