When I put Kadees on an Atlas 2-rail car, I use one of the shims Micro-Mark sells. All of the cars I've done this to have 33" wheels, though, so I'm not sure how a car with 36" wheels will spec out. I like to use the Kadee 745 couplers with the plastic draft boxes as they have more give so you can squeeze in the 2mmx8mm screws without cross-threading the holes.
https://www.micromark.com/O-Sc...pler-Shims-Pkg-of-60