[Toivo]

It probably won't run that hot, as long as he didn't fill it so far that no coolant can flow through it at all.
The real problem is that it will retain heat, long after you shut it down, and without coolant flowing, that heat will build with no where to go unless you put a timer on your (electric) waterpump/fan combo and have a super battery.

My personal opinion, look for something else, whether it be a 428 block or keep looking for another 427.