Are you aware of any Paleo Hebrew for Psalm 40:6(7) that reads “a body you have prepared?” How much monkey business would attend to altering the characters to read, “my ears you have opened?” Hebrews 10:5 is the only reference to that phrase (”a body I have prepared”), so the surrounding verbiage must be what triggers a concern, since English translations differ so much at that point.
If the King James version was good enough for the Apostles and Paul, it’s good enough for me.
Have you looked?
Secondly, the compilers of the MT sadly targeted and removed or altered scriptures when God didn’t authorize it, as evidenced by far older Dead Sea Scrolls and numerous other older sources reveal this.