Rich Goodale,
From what I have seen of many courses over the years, it appears that the most consistent feature that remains basically intact is:
THE ROUTING.
And there are a number of courses where that has been changed/modified.
But, for the most part, that seems to be the single surviving feature that continues to endure in spite of committees, boards, presidents, architects, tinkerers and owners.
And, with a routing comes the basic design of the 18 components that make up the routing.
Beyond that, I would tend to agree with you, that much has changed over the last 70-80 years at many, if not most, if not all golf courses.
So perhaps the important features of a golf course, that the original architect should be forever connnected to and associated with are the routing and hole composition.
Everything else appears to have morphed over the years.