If you swap from iron block to aluminum block,,,

I was just thinking down the road a ways. Say my engine combo works great but I wanted to lose weight off the nose of the truck. Is it just as easy as purchasing a aluminum block and having it machined? Can you get an aluminum block with sleeves in the .020-.030 over range?

(If I was going to do it down the road I would be adding a supercharger at the same time.)