Check for frozen engine?

I'm looking at picking up a boat in a few days. Already seen it and it seems in decent condition but I'm a little concerned that the engine wasnt properly winterized. I opened the water strainer - just up from the raw water intake and it had water -not antifreeze in it.

I'll be doing a lake trial to check it out and am familiar with these boats. But I havent ever experienced first hand what a frozen block might behave like.

Where should I look for issues - exhaust manifolds, actual block, etc?

I would presume after up to operating temp the issues would be apparent - what would those be - rough idle, over heating?

Cheers