I doubt they can show a properly registered copyright, which would have been required before 1978. I doubt the copyright laws back then would have even allowed copyrighting the shape like that (but I'm not a lawyer). If they can show they registered the copyright correctly under the old laws they would have a copyright case since copyright applies even if they are generic.
Also, since the shape has functional aspects (see others), patents would be the correct protection, but the important patents (if any) have expired long ago. You can still patent something today if you make a variation of the shape - but it would be trivial for anyone to work around that patent since the main design is free of patents and a very specific minor change from the common shape it patentable.