Shane,
Bill is right, all of the original 55-57 Headlight Trim Rings are cast pot metal (chromed or painted).
I did buy a set of NOS Headlight assemblies (Bucket, T-3 Headlight and Trim Rings) in the original Chevrolet box and the trim rings are Chrome over plastic. I suspect they are replacement parts made in the late 60's.
Mike B
