I've seen the odd unopened pack of these pop up from time to time but have never come across a whole box of them before, so I put a bid in and ended up winning by a hair.
The packs are made of paper and decorated with the team logos. They are stapled shut at the top end. This looks like it would invite cherry-pickers to try to pry open the tops and have a peak at the cards but its not possible to do this (I tried, they are in there pretty good)!
So there you have it, probably this is the coolest vintage thing that I have in my collection now. I have not opened any of the pack in this nor do I intend to - they've survived almost 40 years in this condition and it would be almost sacrilegious to open them, given how few probably are out there. Also the cards themselves are, while not super common, definitely obtainable for a reasonable price.
I do really want to open them though. It just feels weird trying to leave packs unopened. I am going to have to work hard at this.
For a great write up about all of the Yamakatsu sets of the late 70s-early 80s, see NPB Guy's article here.