The reference points for mounting the brace is that you want it as far rearwards as it will go; this leaves the tips of the brace poking out rearwards; just cut them flush.
The forward mounting (the just off-vertical one) has a flat panel with a column either side; the RH side column needs to be profiled and fitted with an infill to avoid shock horror issues.
Just grind the front to an angle, leave the top intact but relieve it about 10mm at the bottom, just weld an infill plate over the hole.
It doesn't show, looks neat,
and does the job.
You can see what I mean when you study Marty's picture, that's one of mine: "here's one I did earlier"
Your Storm hugger won't fit, but get one for a Blade of the same model and it'll go straight on, you'll just need to get a chain run protector for the exposed bit of chain top run by your left boot when riding.
And you need to also use a Blade rear caliper mount.
The sliding stay is the wrong gender, standard is female but the Blade one needs a male section, carefully cut through the welds on your donor Blade arm and have it reattached to the braced arm.
It's easier to get the alignment right if you temporarily fit the rear wheel spindle and Blade caliper mount, that gives you the alignment you need.
It's not falling off, it's an upgrade opportunity.