3D printed body parts? Anyone tried?

Yeah, at this point in the technology it is more suited to smaller non-structural items. Arm rest bases would be a good example, if they weren't already being repopped. The small 69 'Cuda' hood scoops might be a good candidate, but again, you can already buy them. To make it cost-effective, it would need to be a part that is otherwise unavailable. But one use for it is to make molds for casting metal objects. Say there is a hood ornament on your '39 Hudson that is broken and you can't find one anywhere, or you need a piston for a 1914 Stearns-Knight. If you can borrow an original to scan, you can have it 3D printed in plastic as a mold for metal casting. General Dynamics can 3D print titanium jet engine parts, but that isn't an affordable option for the rest of us.