Unfortunately it is not a streait swap. Fortunately there are a lot of things in your favor though. The bottom headset bearing is the same internal diameter and height of the XT (only external diameter is larger). This means you can use the XT lower bearing. The upper bearing is a smaller ID and ED than the DR. This means you need to get the stem machined to fit the upper bearing.
This whole set up slightly rakes the bike out and only highlights how shit the rear shock is.