Posted By:
davidcyclebackI had some very similar aluminum items for 1962 Topps football cards and they came from the 1989 Topps Archive Auction. They were referred to as proofs. I suspect they're scarce as I rarely see them.
If yours says light blue on back, it seem yours is a printing plate. It should be rare, as you rarely see any printing plates for 1950s-80s baseball cards. I don't recall seeing a Bazooka printing plate before.
In practice, lithograph printers often or even usually 'whiped' the plates clean when they were done so they could use the metal for a new printing project. This explains you rarely see old lithograph printing plates, even for newer stuff like 1989 Upper Deck or 1987 Fleer. They wanted the metal for new projects.