When you fill the block w/ hard block then you have no way to drain the block of water unless you drill and tap another hole above the hard block on the side of the block . If it is a race or river boat you still want to be able to drain the block of sand and water as the block will rust and aluminum will corrode away. No protection because of not using coolant (green stuff). As far as the cooling, It would probably be fine. The lower half of the block is more for cooling the oil as it drains back into the pan.
It is mainly only for race applications.