Magnum slug weight vs...

Id like to revive this thread as i am looking into putting a new motor together for my dakota. I have read through the 5.9 magnum sledgehammer article and see that they claim the ic741 is a weight matched drop in piston for a 5.9 mag requiring no balancing. When you look at the listed weights of that piston vs stock mag stuff the numbers dont match up. Can anybody shed some light as to what was done to make this happen or am i missing something?