For those commenting on Iron blocks having something like 70lbs. more weight than an Aluminum version with similar discplacment- It really isn't THAT much. Iron is tougher than Aluminum - you can use less of it, while keeping equal stregth. The relationship isn't 1 to 1 here, there will be a little extra weight on the Iron block, but not 70lbs worth, unless Mazda engineers got sloppy.

I recently took a look at the 2.0L block off a 1999 Alfa Romeo 156 TS - Iron block. You wouldn't believe how tiny it is!