I've heard they are lighter, too, but my gut says that is false. Block sure seems to have to weight more with the full skirts and enclosed cam tunnel. But I don't have anything to refute the claim either.
If it was designed with Finite Element Analysis which existed in the 1990s it should be much stronger than LA/Magnum blocks without having to weigh more. Also remember the heads are aluminum, they are physically bigger than a wedge but the material makes them lighter overall. Even so I'm pretty sure a wedge-head SBM with aluminum top end still weighs less than a G3 Hemi.
I think a big "fail" for Chrysler was never making a production aluminum-block version for cars like GM did with the LQ/LS.
