Gary Lewis wrote
That is one of the vacuum reservoir styles. You can see some of them on our page at Documentation/Vacuum Systems/Vacuum Reservoirs.
Well, I'm continuously learning new things here, thanks!
Sincerely, I would have bet that this was a nice DIY job done by a brilliant and resourceful amateur.
But an OEM designed by an engineer...
Jeff / 1984 F350 Crew Cab 4x4/5.8L w351 4V/ T18/ D50 4.10 front/ 8' bed.
Restored 2019-2022.
Nicknamed «Big Brother 1984», due to its soooo-looong shape & nod to George Orwell's 1984 famous novel.