How to Blueprint your RDX, check out this link http://www.corallyusa.com/2005/blueprint.htm

Its old but it has some great reading on diffs and shocks.

ZMANN i do know the old RDX diff fits the PHI so i cant see any reason why the new diff wouldnt fit the old car.

MAZMO The PHI was designed to have a LOT of steering, this is probably the one main reason it has been so dominant, this may not always be to everyones liking. Sway bars do help alot with settling the car down. You may also want to try a shorter front link.

...Ari