Table Mount Squaring Order of Operations Help for First Time Setup

I’ve got a Chicken vs Egg situation that I’m sure many of you seasoned pro’s know the answer to. I’m mounting my y-axis legs on top of 5” wide strips of 3/4” MDF that will be the same height as my spoil board (strips of MDF with t-tracks running in between). Where I’m getting stuck is that I know I need to square my machine first and then follow up with adding in the spoil board/t-tracks, BUT the machine is first being mounted to the 5” MDF strips on each end that subsequently need to be squared to the machine AFTER it has been squared up. How do you go about this order of operations when you’re squaring separate systems that rely on each other, but have no initial reference point.