   The inaugural Fifth Avenue Auto Showcase was well-populated when I arrived 15 minutes before the official opening at noon, Oct. 11. Three blocks of Fifth Avenue from E to Market streets were closed to traffic to showcase three &ldquo;salons,&rdquo; or groupings of cars: Exotics, American muscle and specialty vehicles, which included a show-stopping 1946 Flexible Clipper bus restored and converted to a motor home. 