Let's make this perfectly clear. As much as Mustang fans (this author included) would like it to be otherwise, the 2010 Shelby GT500 does not use an aluminum block. At least a couple of times over the past few weeks, there have been online reports that the cast iron block of the last generation has been ditched in favor of the lighter material. These reports are incorrect.
At the Ford preview briefing just before Christmas, we explicitly asked SVT chief engineer Jamal Hameedi if the block had changed, and he told us that it remains iron. When the aluminum rumor popped up yet again yesterday, we contacted Ford spokesman Alan Hall, who repeated the iron refrain. Whatever Ford's reasoning was for keeping the hood closed on the GT500s at the Detroit Auto Show, it is not because they were hiding an aluminum block. The reason for the iron block is that the aluminum unit from the Ford GT is designed for a dry sump lubrication system and there is nowhere to package the oil reservoir in the production Mustang.
[Sources: Ford, The Mustang Source]