Maybe Lanner (flat) is referring to the 87+ rotors (the ones with the 100mm hat height) that have 50mm pad area height even though they are 20.5mm width - I am told this, did not measure myself.
The 289x20.5x71mm rotors have about 46mm pad area height. The 986 rear pad has a height of about 48.5mm so it overhangs a bit.
effvee I uploaded some photos.
My calipers are not yet attached. I put them on just to see but for the rears there is no room for the whole brake pad.
Front:
Back:
Top (see the overhang, about 2.5mm):
kai4130 please report back.
addition: The Boxster rear rotor will not clear the handbrake shoes and hub and the Boxster S rear rotor has a bore of 98mm instead of 103mm that we need, so it requires some machining there. xD It also has a height of 67mm instead of 71mm.