On my Interceptor, I replicated the factory brace with thicker flat bar stock. Then cut out a channel in fender to bolt it in from underneath. Imagine flat piece of metal 3x thicker.
However, the ninjette doesn't have any bosses to easily bolt on brace. We'll have to clamp it around outside of sliders. Here's Telefix unit.
Would be easier to have solid centre section between fork tubes. Then just bolt in end-caps. All we need to measure is:
- outer diameter of fork sliders
- their center-to-center spacing
Do you have Solidworks? I guess any 2D drawing programme would work.