Why screw around with casting engine blocks out of molten metal when you can carve one out of a solid billet of aluminum? For one thing you would likely need a Matsuura 5-Axis Mill. The crew over at Toolmonger posted up this video of the 5-Axis in action, in case you're thinking about picking up one of these babies for the backyard instead of a that BBQ patio set. [Thanks to Jon for the tip]
Definitely second you guys on the up-front CAD work to do this. When I saw it on TM, I figured a month for the CAM programming, after the months/years to design the block itself. What do you think the actual runtime was on the mill? Days? Week(s?)? We only saw 8 minutes of it but it had to have been a vvvvvvvvvvvvvveeeeeeeeeeerrrrr... long program.