Hey found this
http://www.trucktrend.com/features/t...nes/index.html
They put a Duramax and Allison into a 1989 1500 4x4 and ended with a curb weight of 4700lbs. Sounds to me like the Durmax isnt as heavy as I first thought.
After looking at pictures of them on Banks website The block does not look all that different from the LS engines. Although it is probably a little beefier and i am sure the heads are heavier than ls heads, I think it maybe close in weight to a big block chevy with iron heads, which isnt that great but isnt that bad at the same time.