That's a really nice torque arm, but torque arms are best in tension mode. If the load causes it to twist or bend, it can result in a locked up rear brake. The simplest set up is located on a peg in the swingarm, but if it needs a torque arm, it's better to have it in tension.
We had an RS125 racer years ago with a skinny little torque arm (in tension). The early GS 4 cylinder Suzukis used a 3/4" tube in compression, but a large diameter tube can handle more twisting/bending load than a thin rod. The larger the diameter, the greater the load it can carry, so a large diameter tube is stiffer than a small diameter rod.
How as the caliper retained on teh KTM wheel/swingarm combo and can that be replicated.