Solely? Authors who write for a living write lots of books, not rely on one.
There are many ways that such scholars can get paid. For example, they may get hired to be professors and teach it in a college. They may be hired to authenticate alleged Dylan memorabilia. They may get hired as expert witnesses in a legal dispute over it. They may get hired as appraisers when auctioning/insuring the stuff. They may get hired by museums to curate, organize, and present a display of Dylan stuff. Etc.
The poster was talking about 'jobs like this' , not about this specific job.
Even if there was an answer to your question it would not really be that informative because we are talking about a future with more automation, not the current state where most people do not have as much free time or energy.
Jobs? People will study his notebooks for free. Are you going to pay for the album they put out from the inspiration they took in afterwards?
Do you think Wilentz made a living solely on the book, “Bob Dylan in America”