It never freezes! Volvo 240 and no anti-freeze = ??

Note: Save the preaching I know I screwed up :(

Here in Portland Oregon we've had quite the cold spell and it didn't dawn on me until too late my 1977 Volvo 240 didn't have antifreeze. It spontanously leaks water in the summer so I typically just keep a gallon jug in the back seat and refill when needed. Needless to say I refilled too many times during the summer with plain water and depleted the antifreeze ratio. Now the radiator hoses are rock solid with ice and the waterpump is frozen.

What are the chances of the block or some other part cracking and does the 1977 240 have a freeze plug?

Thanks for any info.

-M