And it appears you signed up specifically to answer these questions. I’m curious too. Based on your name I’m guessing you maybe have some interest in urban architecture. It was an interesting old thread to read though, even if many of the links were dead.
Regardless, welcome to the board.
Two of the old millionaire mansions that still exist as museums are still there, unattached – The Frick collection on Central Park East (5th avenue) and J. Pierpont Morgan Library at 5th and 18th.
The other thread mentioned 217th and Park Terrace (W?) near the very north end of the island.
From street view, there are a number of actual single houses at that location.
Since this thread has been brought back from the dead, I think the best example of a “regular” house in Manhattan is 121 Charles Street in the Village.