What is a good source on the relationship between the different texts within Isaiah 40–66?
You have to be more precise.
I am looking at how Isaiah 40-66 is used in the NT.
Have a look at the New Teatament Use of the Old Testament interactive and see if that helps.
https://www.logos.com/product/5321/commentary-on-the-new-testament-use-of-the-old-testament and
https://www.logos.com/product/37663/handbook-on-the-new-testament-use-of-the-old-testament-exegesis-and-interpretation
Edit:Possibly important to your thesis is
https://www.logos.com/product/45778/typos-the-typological-interpretation-of-the-old-testament-in-the-new
