I have a 2000 XR600R with an XR's Only tail rack. I wanted better carrying capacity without side bags because I ride a lot of single track. The 1400 Series Pelican Case has the same width on the short side as the rack. The 1200 Series has the same width on the long side. I got one of each from Santa. 1200 for trail rides, and 1400 for longer trips.
The rack has existing mounting holes for the stock tail bag. 1200 Case:
I used three bolts with rubber between the rack and the case and a 1/8" aluminum plate (6" x 8") with lockwashers inside the case. The rubber holds the bolts in place for easy switching of cases and also seals the holes. With the foam packing in place the mounting system is out of the way.
The rack is symmetrical so I flipped it 180 degrees so the case would be towards the back.
For the 1400 case I used the same hardware except for an 8" x 10" aluminum mounting plate. 1400 case:
I also have a Wolfman tail bag that can be strapped on top of the 1400 case. It's almost exactly the same size as the 1400. Can't wait to try them out!