Generally don't have a lot of time to work this jam but the deadline is a little more lenient I can squeeze a small game in. While the theme implies the setting of 70s-90s and beyond at least for the mascots I like the idea of a 70s restaurant chain being hopelessly tied to the 60s with Jambon being a Beatnik. Sorta like A&W using a classic Hanna-Barberra branding.
Gathering up a moodboard of 60s graphic design and the trends at the time, I see a lot of teals, browns, orange, and swirls it sometimes blends in the 70s territory with how surreal the choices can be but still has the post-WW2 optimism that the 50s had. I'd like to really go into the spy aesthetic. Whether the secret government research is a branding or actuality I'd like delve into the conspiratorial/paranoia aspect that seems to plague most of the Cold War era.
Then I realized that, fast food chains in the 50s and 60s also had a boom in car culture due to the highway being more prominent. Fast foods would often have drive ins where you could eat at your car. Sometimes it wasn't about the food but to show off your new ride at a typical hangout for teens. I recall my grandparents talking about how their friends wanted to work at A&W just so they could roller skate food over.
One thing I'm noticing the most is the absolute over elaboration on signage. In excess the American highway seems like a giant drive-thru mall full of wonders. So I think I'll set the game in this particular location.
So to keep the game simple I'm going to have it be a first person game where you're stuck in a car and can't really move. Instead you're spying on customers and passerby's that go into the restaurant. I haven't really thought about the how or whys of it, but generally want to communicate a contradictory state of optimism and paranoia. 
Right now I just have mouse control tied to camera turning and some colored cubes. Grabbed a free 3d model of van that was vaguely 60s enough. Though very hard to find cars of a specific period of low poly so might have to make them myself.
All I got for now.