I don't know about the state of affairs in 1967 but around 1970 the technology was pretty much common-place, it seems. I vividly remember such 3D picture cards as giveaways for kids at gas stations (in particular, Shell) and supermarkets. By the beginning of the 70s, at least, the production costs cannot have been super-high any longer, otherwise they hadn't thrown the 3Ds at you nearly everywhere.
I guess that in the second half of the 60s, record companies realised that record covers help sell records, and possibly more than they had thought. Just consider record sleeves in the early 70s such as the zipper sleeve of Sticky Fingers (I always wondered what that one
cost), or the packaging of albums such as ELP's Brain Salad Surgery. You wouldn't get such efforts today with regular releases. I'm sure quite a bunch of people bought Sticky Fingers because they wanted to have that album with the zipper cover (apart from the fact that the music on it wasn't all too bad either