updating to 1.21.4

Hi,
I am finally starting the process of updating my server to 1.21.4. I have a resource pack on there that is using custom model data and I don't want to have to swap out all the items that all my players have with new ones using the item_model. I do see that the items still have the custom item model number on them when updating the world to 1.21.4. It is now under float. How do I use that in the json for my items. Google hasn't been much help with this.