A bit of both.
According to what I could find the bolt points are in the same spots. It is literally a direct swap-out. But its casing is modified to be stonger but thinner and lighter. The internals are beefier. The gears are supposed to be thicker, to handle the extra torque.
Tremec doesn't have any data up on their site yet but
http://media.gm.com/us/powertrain/en...08_MM6_MZ6.doc