That is Space Launch System (SLS) booster integration engineering — blending old and new systems to create a superior booster.
Made It Possible: Matt Mecham and Becoming a Booster Archaeologist
Robert and Empowering Future Rocket Scientists
If you would have told me when I was a young boy growing up on a Colorado dairy farm that I would get the opportunity to design, build and test rocket motors for a living, I never would have believed you.