Michael -
I don't know if you know much about your great-great-grandfather's history, but if you are interested in learning more, start here:
https://www.keeneland.com/keeneland-library
Unfortunately closed indefinitely due to COVID but will open again and some point. The Keeneland organization is supremely well funded.
They are basically the Library of Congress for horse racing and the librarians here love to help people do research. I'm in the horse business and my "sort of in-laws" let it slip that his great grandfather was a jockey but he didn't know anything about his career. I was able to find out he was actually quite good for a couple of years before a serious injury.
Good luck on your card search.