Unidentified possible Indy 500 footage - Al Unser - Mario Andretti

Description: Don't know much about this - it's silent unfortunately and I received it with my previous batch of commercials. It looks like footage from a practice at Indianapolis from the late 1960's - I'm sure a commenter will have a better idea of the year. From a 16mm print

Online Copy: https://www.youtube.com/watch?v=HRQj66DAYX0

Metadata Source:YouTube