I agree with your concern/desire to move that 6 hr block to middle of night. I agree with pp that sleep patterns will probably be changing here soon.
I wouldn't worry so much about the cluster, and just work on the df. I was doing both with my lo at that age, but she got to taking very little at both cluster feeds, so I dropped one. The df, though, I still do and I think it took a few weeks to see the difference. That said, she hardly would take anything, so I started waking her and changing her diaper, reswaddle then feed. She'd take more that way. After doing that for about a week, I can now df without waking (I think maybe her clock is now expecting to eat then ??) so she feeds better, even in her sleep at that hour. Try it for a week or even two. That may be hard if you'd rather go to bed before then, but experiment for a few weeks and give it a chance to make a difference.