Big blocks (cast iron block) weigh in about 600-700 depending on how they are dressed and options. Dmax engines are 900-1100 depending on what you call "dressed". All without the Allison
The 6.5 was essentially a modified small block. Same ballpark weight as a small block.
The allison weighs 330 dry. 4L80E about 150 dry.
A 6.5 weighs in around 675 IIRC with a turbo. It definately isn't based off a small block as I've got one sitting out in the shop, but I'll agree it isn't quite asd large as a big block. An iron block 454 vortec is said to weigh around 750 or so. I know that the DMAX/ALLISON package only adds 275 pounds over a 6.5/4L80E package as both myself and Gordon just down the road from me have both done DMAX swaps in our GMT-400 SUBURBANS, and we both saw weight gains of about 275-300 pounds for both trucks. I know the ALLISON is about 150 pounds of that weight gain as well. When I was researching my swap the weight I found for an LB7 was right around 825 pounds which supports my weight gains after the swap.