It looks like you have a Cyklon Super on your hands, probably dating from the early 1980s; or even the 300, judging from those polymer second stages, provided that they hadn't been swapped out.
The upside is that, while those models were discontinued in 1993 (to be replaced by the balanced Cyklon 5000), parts kits are still available from Poseidon; so too, standardized adaptors for the original hoses, from their original "British Railroad Thread."
Cyklon and Jetstream first stages were originally fitted with either a metal or rubber environmental cap, filled with vodka or some alcohol / glycerin concoction, etc. to prevent freezing (see photo) -- and those accessories are still available, decades later, and very effective -- and were even used by Cousteau and his team while in Antarctica.
I took my Cyklon 300s to freezing or near freezing conditions, on any number of occasions over the years, without issue . . .