Can you recount Kakasaheb Dixit's vision of Vitthal and how Baba confirmed its authenticity?

Certainly. As narrated in Chapter 4, Kakasaheb Dixit had a vision of Lord Vitthal while in meditation after his morning bath. When he went for Sai Baba's darshan later, Baba surprised him by asking, "Vitthal Patil had come, right? Did you meet him?" Baba even added a playful warning to "nail him down and make him steady" as he is a "big runaway." The confirmation became even more profound that afternoon when a vendor arrived selling pictures of Vitthal, and one of them was an exact match to the form Kakasaheb had seen in his vision. This incident, as described in Chapter 4, left Dixit amazed and deeply reinforced his faith in Baba's omniscience.