Here is a video that Danny posted a couple years ago.
You can see in this video the yellow butter clearly separate from the pale white buttermilk, so he must have had his cream close to room temperature.
Sometimes you can get fancy smaller glass jars in the canning section, they make them a bit better looking as people sometimes give a jar of homemade jam as gifts in the fall.
Hobby Lobby has quite a vast selection of decorative glass jars as well in all shapes and sizes, then ebay would have the vintage looking jars.
I was also thinking it's not mandatory for the jar to flip end over end...you could spin it like in a lathe? Imagine if you had the lid chucked in a lathe, then thread the jar on, this would run more smoothly, but you would need to mount some sort of beater inside the jar so as it spins the beater would spin with the jar to do the work to the cream, it could be as simple as a single flat plate on one side so as the jar spins with maybe 5/8 full of cream the flat bar comes around and mixes the cream. I only mention this as it gives you more mounting options in your bearing towers.
If you really want to get Olde Timey? you could make a unit with a vertical plunger motion...very much like the Ertl Pump Jack, then you could make the really old "dasher" style butter maker.
Lots of ways to get the job done, I suspect Bruce's SPS version will be super sweet!