OK maybe not. I'm not the one that put these brackets in. The more photos I google search of 12 bolt rears the more confused I get, pardon my inexperience here.
To me a 9" is about like a power glide, its really good once everything is upgraded. Some ppl like having a second 3rd member to swap gears out.....but a second 3rd member isn't cheap........and isn't really any faster to swap out than a second carrier and gear set in an 8.5 or 12 bolt........once it's set up the first time the swap over is pretty painless.......and alot cheaper and easier to bring along........ 9" does eat a little more power than 8.5 or 12 bolt, but it does have more contact area between the pinion gear and ring gear.
If you cut the inner shock mount off their housing,that should work,but I can’t confirm that without actually having one in my hands. They have a double shock mount with one set of holes in stock location,and a second set moved inboard,behind the lower control arm,to take some of the angle off the shock for better 60fts and better shock performance.
So I crawled underneath and measured the distance between the diff housing and the inside face of the brake backing plate. About 18.75" for both sides.
