Did all the 64 Darts come with Spark Plug Tubes?

All slant-6 heads made through the 1974 model year had the spark plug tubes, yes. The '75-up heads have no plug tubes and use a smaller, taper-seat spark plug. Plug access is generally clear and easy no matter which head you have, so I'm not sure what difficulty you are encountering getting a tool onto the spark plug. Make sure you're using the correct socket.