'54 could very well be the turning point George, or '55 or '56
for that matter. It just seems logical to assume that when GM
was switching over from fat fenders to their cubism design
that many changes were taking place. That mid 50's period of
time is filled with much uncertainty. The later parts books,
mine as shown in the link, was a May, 1977 revision, list the
same number from '54 thru '72. Just because the parts book
list's them for those years does not mean that the original ones
came with a black chain. That could have started in any year,
the parts book is for "replacement" parts, it never guarantied
that they would be exactly like the factory originals, just
that they would fit like the original parts.
In fact if I recall correctly, at one time GM only specified
that replacement parts would only be guarantied for 10 years.
Of course many of the parts fit the same application for many
decades.
DG
