The cases for the NTX are made by SW mototech. The factory topcase is difficult to obtain and is identical to the standard SWM case offered HERE
The case attachement is by the universal plate below. This plate uses clamps to hold it to the factory rack. The slots and holes in this plate do not line up with the factory rack holes very well:
A revised version of my original plate in a previous blog post is shown below with holes for topcase mounting:
The topcase latch required the removal of the center bent tab while still allowing the rack to be used as a tie down point when the box is removed. Rack mounted to the motorcycle after the factory plastic cover has been removed:
A possible change will be to mount an alternate set of holes allowing the plate to be moved slightly rearward to allow more room for a rear rider. A backrest pad is the next to be added.