Alan,hi...
Thanks for your care...
I read about this....
But how is this device?
It would be a pin with a ball on the point?
In texts, this junction is quoted as being non-detachable ...
This pivot pin is screwed ?
Anyway, I can forget the idea of making a fifth-wheel,
do you agree?

This would be a junction type coupled ...
If I did not find anything, I just do a ball-pin type pivot, articulating the
trailer on the rear axle of Bedford...
Like this:

Regards and all the best !!!