This design is one little thought of reason why GM and other manufacturers have trouble with blown head gaskets.
Not having head bolt bosses that go all the way down to the lower crankcase allows the head decks to flex as they heat and cool. This flexing/bulging, combined with the pressures of combustion, breaks the gasket bond over a period of time. Kind of like putting hot water in a milk bottle and putting the lid on. The bottle will start to bulge as pressure increases. Put the same bottle in cold water and it will pull its flat surfaces in. Having the bolts go all the way to the bottom end stabilizes the head deck and keeps flexing down to a minimum.
Also little known problem is aluminum heads on cast iron blocks. Aluminum expands and contracts almost twice as far as cast iron when it heats and cools. This also breaks the gasket bonds faster.