Travel back to a kinder, simpler time when Wagon Queen Family Trucksters ruled the roads, dead people got strapped onto the roof, and Chevy Chase was actually funny. Very funny. Whether dancing with a sandwich, skinny-dipping with a supermodel, or punching a moose in the face, Chase, as Clark Griswold, finally lived up to all that early ''SNL'' promise. (Then again, his success as the dim-witted dad also led to a series of wildly uneven sequels culminating in ''Vegas Vacation,'' so our feelings remain mixed.) One would hope that a special edition of the ultimate road comedy, National Lampoon's Vacation 20th Anniversary Special Edition would contain miles of extras, but this ride stalls a bit. In one of a series of short interviews, Dana Barron explains why she and Anthony Michael Hall didn't go on the ''European Vacation,'' and in the cast and crew commentary track, director Harold Ramis talks all about the original ending (played to test audiences) where the Griswolds take Roy Walley hostage. Cool! So where the hell is it?