You can't just compare a Mag lower though - there would never be "just" the lower - because the hub, spindle, springs, etc all are attached the the lowers on a "conventional" fork so all count towards unsprung mass.
And the hub, axle and internals aren't attached to the unsprung mass on a inverted fork??? If anything most of those items would be heavier on the inverted fork.
Also with the inverted fork there has to be a dropout to slider interface which wouldn't be needed on a conventional fork. I'd still put money on the conventional fork having lower unsprung.
cynic-al, unsprung has more effect the lighter the sprung mass.