Hi Tom. I can't find any interviews or articles about the creation of Hawkeye. Other character's Wikipedia entries usually have brief statements from the writer and artist about what inspired them to be created. For Hawkeye though, I can find nothing from Stan Lee or Don Heck. Have you spoken to Stan or do you have any inside information? I really love his early Avengers appearances, and the fact that he was almost an antagonist to Captain America. Very original in my opinion.
I don’t really have any particular inside information on this, I’m afraid. Even the question of who designed the costume is unclear. But I doubt it was much more complicated than them needing somebody to fight Iron Man that month, and thinking the gimmick of an archer would work.