Of course most East European nations are now members of the EU and so they operate under the same copyright term as the UK namely, the lifetime of the artist plus 70 years. The two major non-EU nations in Eastern Europe (leaving aside Russia) are Belarus (lifetime + 50 years) and Ukraine (lifetime + 70 years). The third state is Moldova, about whose copyright laws I know absolutely nothing. From this we can deduce that any work made in the 1960s will still be in copyright everywhere, unless the artist died within the seven or so years after the completion of the work, in which case copyright might possibly have expired in Belarus.
In all these countries, the employer will be the owner of the copyright.There are provisions for anonymous works, but generally speaking with the exception of Belarus, the copyright protection in such cases can be sumarised as lasting for 70 years from the date of publication. Again this would mean that the artistic design remains in copyright today.
Clearly you would face an enormous and costly task trying to track down the identity of either the artist (to determine his or her date of death) or the company which formerly owned the copyright. In theory you can use the IPO's Orphan Works* licensing scheme
to obtain a licence to use the artistic design in the UK, but I suspect you may not be able to meet the diligent search criteria sufficientally well for a licence to be issued. Nonetheless, it might be worth discussing the problem with the IPO. email@example.com
The tempting alternative is to just go ahead and use the design, and wait to see if you are challenged. This is not something I would normally suggest, but given the ephemeral nature of the original product and the likelihood of ever finding the author or copyright owner to ask permission, this may be a risk worth taking.
*There is a separate EU-wide system
for using orphan works but unfortunately it isn't available in this case because, a) it only applies to institutions such as museums and libraries, b) the works once licensed can't be used commercially, and c) it doesn't apply to artistic works.