If you can crack an iron block then im sure aluminum won't be any better as far as strength goes.
anyone ever crack an iron block cyl wall? well i did - PerformanceTrucks.net Forums

Plus if you go to LS1tech.com and type in cracked aluminum block in the search, you'll find many MANY people with cracked block posted up there. And they are ls1 cars. Too much power can crack any block, but an aluminum block with 5000lbs load on it will crack much easier than an iron block