hi @nmclain and @alankemsley I had to jump back to this request as at first is not marked as solved and at second I would like to clear one thing that there is no need to write custom code if content is not pulled from CMS. Here is short video where I show how things can be done.
I have forget to add third option as I have promised to get back when I talk about CSS Grid. What I had in my mind that you can combine CSS Grid and Flex. In Grid you can introduce extra div element and place part-2 and part-3 inside this div element. After set this div wrapper as flex to be able swap positions. Of course you have to adjust Grid Area to this scenario. Hope that make sense.
@nmclain if you do not have further questions related to this topic feel free to close it as solved