Frame is post mount?
i'm afraid you're wrong. The frame is IS mount.
The brakes will fit fine, and 180mm will be perfect.
Look at this, then perhaps edit your post ;-)

Ya, OK, I'm being smart arse at your expense ;-)
They changed them in 08, they're now postmount 200/203mm. So you'll need a bigger rotor and just bolt the caliper straight on, don't use the adaptor.
(If this turns out to be wrong, which it could be as i don't look after the DH end of things, sorry!)