I made an articulation coupling like this, if it helps:

The piece in the middle of the upper picture is a bolt with a loose sleeve over it made of two pieces of telescopic brass tube and a washer, the inner piece of tube protrudes downwards into the middle bogie with the ride height set by the washer soldered at the bottom of the  outer (shorter) piece of tube.  The lower picture shows how the bolt (with the sleeve over it) screws into a tapped hole in the bracket on one coach.  The bracket on the other coach is a clearance fit over the bolt and that coach just drops over the other one.