In general, the fork brace is too skinny to keep one side the same height as the other. The axle will do a much better job of that.
Now that being said... keeping the two sliders in sync side to side and fore and aft are the real benefit to the fork brace. It literally doubles the strength of each slider. When you brake, one slider is twisted, the fork brake prevents the wheel from turning to the left by keeping the sliders aligned. On groovy roads, when the wheel takes off from side to side, the sliders act together rather than twisting like a pretzel.
The brace can be made this way... but will take a few tries and may take many. It will be difficult to drill all the way thru the edge for the clamping bolts w/o drifting to 1 side or the other. And getting the fork nests the exact distance apart won't be easy, don't kid yourself on this 1, it has to be dead nuts. Cut a pilot hole for both sides and make a sanding drum a little smaller than the fork. Fit 1 side then the other, this will give you the opportunity to match the spread.
Or design a little adjustability into it.
You don't need a whole lot of adjustment, so oversized thru holes for the bolts could work. Just require a bit of attention during the final fitting to get the ends matched up. And I would plug the open end of the threaded holes, keeps sh!t out and looks better.