At the moment, it's not possible to use custom models for the cars without replacing a existing blocks.

Minecraft 1.16.4 introduces custom ids for Items, which allows customized models to be used without overwriting any other blocks or items.

To make use of this, CarZ could teleport a armor stand with the cart. The armor stand could carry the cart on it's head with a custom model id and rotate depending on how the car moves around. I know it's not the best way of doing it, but in my case, replacing an existing block is not really an option on a survival server. I tought tought that would be a great way of adding that in, even tought it requires two entities.

Greetings, keep your great work up. 👍