I just finished converting a 2005 Volvo VNL 630, it included the removal of the differential axle, the placement of the drive axle in the place of the differential axle and the shortening of the frame. Ensure the shortening of the frame is done by a certified shop because if not it may present a problem later on with registering the vehicle! the drive shaft had also been extended because of the differential housing.
There is a lot of information out on the net, escapees.com, and "red Rover" the truck, also there are several other persons who have a lot of good information on the subject!
I added a lot of excess equipment to my truck such as the MaxBrake, tire pressure monitors, back up camera, Jackeloopy wiring conversion, GPS etc. I took my first trip last May and had a beautiful ride, much more comfortable than the Dodge dually 3500 I had been using before! I felt in control for the first time, especially going down hill with our forty foot trailer. I'll try to post some pictures soon as I am new to this forum and am very happy about my rig! Hope this helps. RR.