Those are "specialty" cars so there's not a clear path to upgrades. Also, with the shortages, upgrades are far from what they used to be. Even as a CHM, I'm often getting a Passat/300/Explorer/etc when booking full or SUV.

The philosophy that I've always followed (and it's even more true at this point):
1. Book what you need and are willing to pay for.
2. If you just 'want' something, book full or intermediate. Then ask for upgrades when you get there. I've only seen one GT in the last few months. There are tons of 300s but not too many Chargers, but maybe you'll get lucky depending when/where you're picking up.