I'd like to think Indy is bigger than Daytona, and I personally believe it is - to true race fans and in meaning - but Daytona (sadly) continues to get better TV ratings...
It was "easier" for outside drivers to run Indy back in the day, as it was on Memorial Day, which was on May 30/31 until like 1971; so they weren't up against other races during those times...(as May 30/31 didn't happen to be on a Sunday in the 50s & 60s - at least...)
& it was part of the "f-1" circuit from 1950-1960, and in the 60s, it looks like the only conflict woulda been in 1965...
https://en.wikipedia.org/wiki/1961_Formula_One_season
https://en.wikipedia.org/wiki/List_o...is_500_winners
World 100 (in the 60s - 1st year was 1960)
1960 June 19* 89 Joe Lee Johnson Paul McDuffie Chevrolet 400 600 (965.606) 5
06 107.735 Report [15]
1961 May 28 3 David Pearson John Masoni Pontiac 400 600 (965.606) 5
29 111.633 Report [16]
1962 May 27 29 Nelson Stacy Holman-Moody Ford 400 600 (965.606) 4:46:44 125.552 Report [17]
1963 June 2* 28 Fred Lorenzen Holman-Moody Ford 400 600 (965.606) 4
52 132.417 Report [18]
1964 May 24 41 Jim Paschal Petty Enterprises Plymouth 400 600 (965.606) 4:46:14 125.772 Report [19]
1965 May 23 28 Fred Lorenzen Holman-Moody Ford 400 600 (965.606) 4:55:38 121.722 Report [20]
1966 May 22 42 Marvin Panch Petty Enterprises Plymouth 400 600 (965.606) 4
35 135.042 Report [21]
1967 May 28 14 Jim Paschal Frieden Enterprises Plymouth 400 600 (965.606) 4:25:02 135.832 Report [22]
1968 May 26 3 Buddy Baker Ray Fox Dodge 255* 382.5 (615.574) 3:04:14 104.207 Report [23]
1969 May 25 98 LeeRoy Yarbrough Junior Johnson & Associates Mercury 400 600 (965.606) 4
56 134.361 Report [24]
1970 May 24 27 Donnie Allison Banjo Matthews Ford 400 600 (965.606) 4
36 129.68 Report [25]