I body mount my #1 scale Kadee couplers. Getting the coupler centered and aligned correctly has always been a problem for me. So I 3D printed an aligner that puts the screw holes in the center of the car. It also creates a smooth surface from the ouside of the car to mount the kadee. Here’s the link to the adapter.
https://pageshot.net/zbBu8DzV3RccDzwp/www.tinkercad.com
Source: https://www.tinkercad.com/things/3FH6dxAsgZH-5mm-high-kadee-mount-for-bachmann-freight-cars/edit