Does it fall under that Fair Use Act of 1976 to include a song as the intro to a presentation for work if the presentation is being given for educational/teaching purposes?
The educational/teaching purposes do not apply to any copyrighted work that you chose to include in the educative material that you might produce.
The educational/teaching purposes means education refering to or related to the work being used.
If your presentation is about the musical styles of the 70s, you can use a 70s song to show how it matches those styles, its impact, relevance... But you cannot use the same song as soundtrack in a presentation about how to properly fill the X-520 form.
It also usually requires some depth. So, your presentation being just "These are some songs from the 70s" and playing a few hours would not cut it, even if it serves for some in your public to listen (learn) new songs.