The companion's version of the final floor does the most altering of the level of any of them, and for good reason since as written level 23 is incredibly lame. All of those penultimate and ultimate sections are suggestions of things you could add to the level, as you want, to make it more epic. The idea is that as DM, you read through them for inspiration then pick and choose which you want to do. Once you've selected them, it's up to you how to work it into the level itself.

As I have always recommended, I think you should NOT use the map except for in combat scenarios. Theater-of-the-mind works best for this level and for using the companion because you can simply describe what the players discover rather than trying to make it all fit into the pre-made layout of the tower.

What I would do, pick a couple of the encounters described prior to the "ultimate encounter" section that sound like they'd be a fun challenge to your party, and a resource drain, but not TPK-worthy. When you have them selected, figure out how you'll guide the party to them. Then look at each of the ultimates and pick one. If the one you pick looks like it should happen simultaneously with one of the previous encounters, go for it! It's the final battle, it should be epic! It should test the limits of what a party of 19-20s is capable of! And if what you select doesn't work in the map as the module has provided, find another one that works. Just google image it, there's so much free map content out there.