Very good explanation of your issues octane.  I assume you are in a Static Structural analysis. I will also assume that the X axis is along the diagram you sketched and the Y axis is up.

Here is a simple way to model this system. Pick the face on Body B that connects to Body C. Insert a Remote Displacement. The details of the Remote Displacement have the X Y and Z coordinated of the "remote point". By default, those will be at the centroid of the face you picked. Simply type the Global coordinates of the location of the wheel end of Body C. If it is a car, maybe that is 4 m more in the X coordinate that you got. Now to represent the wheel, you can just type a 0 for the Y displacement, leaving all others Free. If you don't want the wheel to go sideways, also type in 0 for the Z displacement.

One change recommended is to change the Behavior from Deformable to Rigid. That means whatever face you picked behaves like a rigid face on the flexible body. If you don't like that, you can try Deformable.

Two of the approaches can be made to work.

1) You can insert a Fixed Joint to connect a face on Body B to the rigid Body C.

2) You can use Bonded Contact between a face on Body B to the vertex on the end of the Beam line body.

Approach 3 won't work because after you remove Body C and use Connection > Beam you don't have a body to connect to, and you don't want to connect to Ground.