I'm not thinking the charcoal rails are going to give you a complete separation of zones. I use fire bricks I found in my yard. Not masonry bricks. They are thinner and longer than that. There's no radiant heat passing them bricks, but then again I'm using this setup on a 26r. I got plenty of space.
I'm gonna say the ultimate solution for your needs is a slow and sear. Next solution would be some fire bricks. Heck...I've used folded up aluminum foil to hang from the grill grate to make a radiant barrier. I've seen someone festoon a barrier with a pizza pan by cutting a section of it off and some slots to go around the grate supports.