There is an interesting article in the NY Times by Hirsch about how he ran Boston 50 years ago - it was the first road race of his life. All you needed to run was to send in $2 and a note from your doctor saying you were fit enough to run the marathon.
Hirsch went on to be head of the NYRR and co-found the NYC Marathon.
https://www.nytimes.com/2019/04/13/sports/boston-marathon-hirsch.html