I think about this a lot.  I never knew it as 'Ivy League'.  More 'Americana' if anything.  Possibly not even that.  When my late father went to New York in 1978 it seemed like a miracle.  There was a song: 'Sensation...  living in America...'  It was still full of mystique.  We'd seen plenty of it on TV and in the cinema.  We'd heard the music, even as children, whether it was snatches of Motown on the radio or someone's elder brother playing Arthur Conley or Otis Redding on some basic record-player in a chilly front room. 
The clothing...  we saw it before we read about it (saw it on-screen), and probably puzzled over it.  That jacket James Dean wore...  the clothes and shoes Monty Clift was photographed in on the cover of the Bosworth paperback...  Tasselled loafers we'd worn at school but they were just 'fashion' as far as we were concerned.  (Around 1973?  Yes, my parents were still together, just).  Warm-up jackets and bowling shirts were discussed if rarely seen.  Levis, again, were a fashion item.  In truth, a lot of what we wore was thrifted, thrown-together crap.  Manchester 1981-83 opened it up slightly - but it was still just 'Americana': windcheaters, boat shoes, sweatshirts.  'Ivy' came much, much later.