1965 was also the year in which Gregory raced in the Indianapolis 500, starting from the back of the grid and working his way up to 5th before being forced to retire due to an engine problem.
1965 tamén foi o ano en que Gregory correu na Indianápolis 500, comezando desde o fondo da grella e traballando ata o quinto posto antes de verse forzado a retirarse debido a un problema de motor.