Kevin I have the Spohn adj 7/8" Pro Touring bar installed in the 86. Spohn along with Marcus (SC&C) developed that bar. https://www.spohn.net/shop/1978-198...e-Rear-Sway-Bar-1978-1987-GM-G-Body.html
It's installed on an 8 1/2" rear which makes install more difficult. On a 9" there should be less of a problem. One of the ears on the 8 1/2 needed to be removed, a 1/2' spacer at the rear mounts had to be added to drop the bar lower. These done so when the bar rotates from ride height to full compression the bar doesn't hit the rear. A talk with Marcus when I had those issues he admitted they test fit the bar on a 7 1/2 and 9" rear, never an 8 1/2''. My mods fixed the problem with interference.
When you install any of these link bars on the market as you change the rate the links will are not vertical in every position. What they want you to do is loosen the U-bolts on the housing and rotate the bar around the rear to put the link in a vertical position again. Being I drag race, full firm, street drive, full soft and autox the bar rate was changed often. Loosening the U-bolts was not something I wanted to do. So new frame mounts were made for the top of the link attachment with three location corresponding to the three holes in the bar. Also a gusset was added and now 5 bolts are used to hold that new bracket in place. Much more substantial, probably overkill, but i know it's not stressing the bracket or frame. To change the rate now all you do is remove the link from one side, move the link to the new holes on the other side and reinstall the link in the other side. No rotating the bar to get the links vertical.
Lance is using the UMI adj bar on a 9", maybe he'll jump in.
For drag racing some will use the big fat link bars. For a street car they are not advisable, way to much rate in the rear.https://www.spohn.net/shop/1978-198...-Body-Pro-Series-Rear-Drag-Sway-Bar.htmlhttps://www.bmrsuspension.com/?page=products&productid=31&superpro=0