Another Mopar Off My Bucket List - Barracuda Fastback

With the right plastic, such as ABS, the 3D printed parts will hold up. You'll be painting or plating them anyways, which will really help the weather resistance. Just don't try to use the sugar-based "plastic" that is used in the el-cheapo printers.

Yes there are 3D scanners available, but nothing a hobbyist could afford.

The way you get the model is you create it with a CAD system, such as Unigraphics, Autodesk, MasterCam, etc... Obviously, there is quite a lot of training involved.

I 3D model jet engine parts where I work, been doing it off and on for 20 years. Still can't do a lot of things I'd like to do with it. Something like those caps are pretty easy to model, but the first thing you always need to do is measure every feature on them. Because without every dimension, there is no way to copy them.