I agree with everyone about welding up the block and then machining it. A couple of reasons, 1, for threading. 2, because the looks of it, the body assembly would protrude to far into the oil galey and hinder flow. also from the looks there should be an o-ring to seal it or something and there would have to be more material to do so.
as for why toyota along with other do it and only seam to do it to Iron block and not aluminum blocks I think is one to be able to run tighter piston to wall clearances to keep the piston cooler to keep it from getting stuck un the bore being that the block will not expand as much and as fast as the piston. I know that the aluminum blocks have iron sleeves, but they are so thin and expand with the block. Second, on a turbo or any heavily abused motor, any help to keep down possible warenty claims, the better. They really have no bennifet on any motor unless it is under constant heavy loads like say a road race car, or in the 2uz because it is a truck and chances are are that it will be 1 carrying a heavy load and or 2 towing, both situations being under sustained heavy loads and hence the reason as to why they have not and show no plans for the 3UZ motor.
