I really think something like that is easier to accomplish than modifying the original brackets, especially given that they’re pretty much always an oily, rusty, spring loaded mess. The bracket arrangement needed is fairly straightforward, as your work shows a couple of straight pieces of stock with some 90° brackets on the end is really all that’s necessary. I ran my own rear brackets for a bit with my ‘70-73 rear bumper, did the same as you and just made them from scrap. With a bit more modification I’m not running factory 70-73 rear brackets.
And yeah, even a very heavy duty bracket arrangement would be lighter than the original shock mounted brackets.