Possible Clues:

• Collaborator of Crosby, Stills and Young
• Writer Ogden
• Pun-prone poet
• He wrote many long years ago
• 'I think that I shall never see / A billboard lovely as a tree' poet
• Humorist who wrote 'Progress might have been all right once, but it has gone on too long'
• Car company that became part of American Motors
• Architect's name has changed
• 'A Beautiful Mind' fellow
• Architect's unopened grate