You know, I admire you for analyzing how to build your own piece, but this one might dictate a time to buck up and and by a manufactured piece. By the time you get the tooling together and perform all the layout, as well as actually try and fabricate the bracket you need......its going to take a long time.
The exacting alignment needed, and it is a brake piece, will be a big deal in terms of getting the proper alignment for fasteners, drilling, redrilling, honing, filing, etc.
You will be getting a serious workout climbing up and down checking the fitting and then making sure all the alignments are correct and the piece is built in the manner it needs to be in terms of strength and application.
Not trying to dissuade you, but more of a been there done that scenario.
