Publication of Packaging
Product packaging, like any other copyrighted material, is considered to be published when copies are distributed to the public or offered for sale. You are correct that material published before March 1, 1989 must contain a notice and the failure to do so places the material in the public domain. (The so-called "savings clause" of the 1909 Copyright Act -- which would apply for works without notice published in 1955 -- would not save the packaging from falling into the public domain.) Even if notice were included, it's unlikely the copyright in this work was renewed and even if it was, you have a strong fair use argument.
Lack of Visible Trademarks
We are confused about your statement that the products contain no visible trademarks. Except for the spate of "generic" products in the late 1970s, all products contain trademarks in some form -- that's what distinguishes them. In some cases, the product's appearance, itself (referred to as trade dress) may be its trademark. Nevertheless, informational (non-competing uses) such as your museum website would not infringe.
Are We Going to Get in Trouble for Publishing Your Question?
Speaking of 'publication,' are you aware that your email contained a notice at the bottom, that says:
This communication (including any attachments) is intended for the use of the intended recipient(s) only and may contain information that is confidential, privileged or legally protected.Just so you know, the Dear Rich staff has disregarded this warning and ignored the tautological errors contained therein. (We already have plenty to worry about here at Dear Rich headquarters.)