Seems to me as though you would have much more work for no gain. You need a pattern of some sort. The "easiest" way I have seen is foam. I have seen a Chevy Vortec block done this way. To look at the foam you would have thought it was the real deal. Pour or inject the molten metal in and the foam goes away. When cooled you have a block ready to machine. Why not just machine it out of a block of metal either manually or CNC? Either way you have to machine it. With the casting you need to machine it twice. Once for the mold and again for the finished product. Plus you have to deal with a foundry furnace and the mold processes. May even weigh more than a machined case. Some day I would like to machine a whole case. Need to retire first so I have all the time I need.