I watched this "Ultimate Factories" show about a month ago and they were at the BMW engine factory. They were talking about how cool the aluminum block was for their I6 motor, and how hard it was to cast. A good 15-20 minutes of the show was about the block. I was surprised when they said that the block ended up weighing 90 lbs. An LS1 block weighs 92. I don't know how accurate the weight they quoted on the show was, but I know the 92 lbs for the LS is accurate.
The Chevy I6 was discussed briefly a couple years ago. I think the issue was that it was too tall. Here's the thread: http://forums.hybridz.org/showthread.php?t=87482 I'm not sure if they ever pinned down the height issue or not. I still remember that Baja truck. Thing sounded insane, like an old F1 car or something.