A vintage Japanese Newspaper!
This was under the wrap on the outside of the shell. It was not glued, tacked, or otherwise secured to the shell. It was not hiding any defects or anything, just placed there, and of course perfectly preserved. It seems odd that would be there, but I'm sure glad it was! What a cool time capsule find! I wonder if one of the factory workers was reading the newspaper and placed it on the wrap and forgot about it? Or, I wonder if they were thinking "I wonder if somebody far in the future will ever take the wrap off these? Maybe I'll put this newspaper in here as a neat stamp of this moment in time".
You can see that the lug holes were drilled through it when the wrap was drilled.
At least I can date this drums accurately, August 19th, 1966! (Picture 3).
I also love the political cartoon (Picture 2) and what appears to be TV listings (Picture 4).