I used two slot connections, one front, one rear, then an additional artificial component for orientation.
The orient component was connected with a pin joint to the car and a parallel constraint to the ground plane.
The pin joint allowed the car to tip up/down but not side to side.
For bonus I added a sine wave to the helix and friction and bumper at end of travel.
Note I used -Z direction for gravity.
Ah, It works and seems simpler, and might allow banking the car (roll angle inward to bahn)
The upper slot connection has free 3 rotational dof for total system of 4 dof.
So the Masse_vorlage spins uncontrolled.
However, maybe? we can do the same as to the CAR, to the Masse_vorlage and make 3 slots + 3 slots.
Then only 1 dof left plus able to control roll of the car with the upper slot curve.
I will try to get this working with the car rolled/banked inward.
Thanks for the challenge.