Ira:
A topic near and dear to any historian.
I've been thinking about your question for a while and have the following from my personal experience.
I've yet to find a diary to help me. Not that it wouldn't be possible, just hasn't happened. I have found a couple scrapbooks from personal collections and from a public source. Port Huron's greens' chair for the 1920s was a big enough personage (knew presidents and governors etc) to leave his papers to the Bentley Library at the University of Michigan in Ann Arbor. So there I found some golf related, but mostly personal info. Your reference to the Tufts shouldn't fail to mention that it isn't just Ross to be found, but many courses where Ross was involved also involved other architects. That has been debated on other threads, even today. So go to the Tufts for the Ross, but if your person of interest ever worked on a course that Ross did or redid you should give that a try. Audrey Moriarty is an angel in disguise and works with all types, professional and otherwise, including me.
The USGA Library and equivalent personnel is a great source. Some on-line, but some you have to go there and spend the time. You can set up appointments in advance and they were very gracious to me. It was fun to spend an hour trying to get their Pine Valley scorecards in yearly order to see the change in yardages with each new architect or Chairman.
I've also had great luck with various Historical Society's. But you have to know that Alison did a course in Seven Hills, Ohio and know where the Seven Hills Historical Society meets, and on what day, and be lucky enough to show up on one of those days. That works if you start with the local library and librarians, they're gold. The ladies there produced a photograph of the course with a couple classic young kids with old clubs. Also a scorecard. The Case Western Reserve Historical Society was also good for all the Cleveland Alison courses including Kirtland, Lost Nation and Seven Hills. Also debates regarding Mayfield's origin can be continued there. A former head of the Cleveland Ladies Association started to write a history of Cleveland golf. What a great find. Once again a little planning and call ahead helps.
So get to your location, find the local library or historical society, and ask questions.
It also helps to know Mike Hurdzan. I can never give him enough credit. He's his own historical society and library in one place.
At least you won't have to spend the 2000 hours in the St Clair County Library in the 1990s looking at broken microfilm through god-awful ancient microfilm readers. Although for the Detroit News it's still the way if you can locate it.
Technology does have its uses.
Anthony