This SDXL Lora can be used for generating first-gen Ford Mustangs. It has been trained using the words "hardtop", "fastback" and "convertible" in the captions so you might have some success nudging it into the desired body shape.

It can be used for both photorealistic images and artwork. Suggested strength is 0.7-1.0, although at the higher end it's likely to turn other cars in the scene into Mustangs as well.