In the case of general parts - say for any car - if I need a wiper blade for my car I have over 100 brands to choose from - I don't think a car maker is able to claim copyright over the majority of the parts on a car, for whatever reason I don't know.
In the specific case of the DeLorean - who do you think is going to sue you? The company went bankrupt. If you were to, for example, try building an entire new car and try to sell 100 of them as a "DeLorean" then the estate of John DeLorean would probably file a complaint, but I would guess even their ownership is questionable - case in point: http://www.trademarkologist.com/2015/02/5283/
- where Stephen Wynne's excessive PR campaign claiming he was building "new" cars landed him in hot water and he settled out of court with Mrs. DeLorean.
In regard to specific parts, I don't believe the IP is owned by anyone. This also applies to the original logos and is often discussed - the "new" DeLorean company in Texas have registered a different version of the DMC logo as theirs, but no-one would be able to re-register the original logos as their own, as they were never sold, and aren't new now. That said, there are plenty of examples where Stephen Wynne's company have complained to enthusiasts who have made anything with the letters "DMC" on them, but from a legal point of view they have no claim to exclusive use of the letters "DMC". Here is the expired trademark for example - https://www.inovia.com/products/directo ... or-company