G Wagen rear wheel fitment?

Putting together the G Wagen 42177 kit and the rear wheel mounts do not sit flush due to light gray drum having protrusions. There’s no other way to mount this that I can see, has anyone else experienced this and have any ideas/advice?

Putting together the G Wagen 42177 kit and the rear wheel mounts do not sit flush due to light gray drum having protrusions. There’s no other way to mount this that I can see, has anyone else experienced this and have any ideas/advice?