My acquisition.

[m_c]

5.5Kw and 380 delta means you'd need one hell of a single phase supply to power them, along with a meaty step-up transformer and inverter.

If it wasn't for the plastic taps, I would of said the tanks were for oil as most vacuum pumps are oil lubricated. Is there any kind of gunk/residue in the tanks?
Anyway, here's my guess-
A - taps, possibly been bodged for some reason, or might of been some kind of cooler loop connection.
B - vent - pump would pump air/oil into the tank, and it's got to get out somewhere
C - Vacuum connection point - pump sucks air in here, and I'd hazard a guess the big housing contains a filter
D - Oil scavenge feed into pump - the pump contiually pulls in oil along with air for lubrication
E - Level tube