Sorry for the confusion - My error. I confused your bike with the earlier TX500 that has nearly identical spoke wheels to the same years RDs. Those bikes have the caliper mounted in front of the fork legs. The 500 had an option for a second disc, so it had mounts for the second caliper and disc. Because of this you could flip the forks to move the calipers behind the legs without also flipping the wheel and thereby keeping the speedometer drive going the right way round. Because the hub with the second disc mount interchanges with the RD hub, you could flip the forks on your RD and swap out the hub for the 500 hub and retain the mechanical speedo drive. This moved the disc to the other side because the RD legs only have the caliper mount on the right leg so flipping the forks moved the mount to the left. Alternatively, you could swap out the right RD leg for a left 500 leg, mount the caliper on the right side behind the leg and keep wheel unaltered.
If you are wondering why this is getting so much attention, it is because moving the caliper(s) behind the leg is a genuine performance upgrade. Those cast iron calipers are crazy heavy (the road race version was identical but aluminum) and moving it behind the fork leg moves it a lot closer to the center of rotation of the steering. This increases the natural frequency of the whole steering assembly. The higher the natural frequency, the higher the speed needed to start the assembly resonating, commonly referred to as speed wobble. Being that it was(is) quite easy to get your RD to go considerably faster than originally intended, speed wobble is a problem and part of the solution is to move the speed wobble to a higher speed - hopefully higher than you can make the bike go. You can do that by reducing the moment of inertia which increases the natural frequency. And that can be done by either reducing the mass of the assembly, or moving the existing mass closer to the center of rotation. So light and close to the steering pivot is the goal. This applies equally to your 500, to all motorcycles specifically and all things in the universe in general. You can also see why a lighter wheel and smaller and thereby lighter tire works toward this goal as well.