Was there any further proof or confirmation of Kakasaheb Dixit's vision of Vitthal?

Yes, there was a remarkable confirmation that same day. According to Chapter 4, following Dixit's morning vision and his conversation with Sai Baba, a person from out of town arrived in the afternoon carrying twenty-five pictures of Vitthal of Pandharpur for sale. The image in the pictures was an exact replica of the form that had appeared to Dixit in his meditation. Amazed by this synchronicity and remembering Baba's words, Dixit lovingly bought one of the pictures and installed it for devotional worship.