What hitch setup is this?

If there are multiple pin sizes they could be a road hazard. If the pin is too small, the jaws will still close and lock behind it, making it pass a "tug test" but without enough positive "tongue weight" the pin could bounce out, especially with an old leaf-spring tractor like ex-Roadway junk. Kind of like if you're pulling a regular hitch-ball type trailer behind a pickup truck and the coupler is designed for a 2" ball but you're using a 1-7/8". I have a 1-7/8" ball on my lawnmower just for moving trailers around the yard when I mow the grass, some of them use 2" balls, but it works around the yard. If I were to use a 1-7/8" ball out on the highway pulling something with a 2" coupler, it would eventually come loose because it would bounce up, even though it would pass a "tug test".

My advice would be to go to a truck stop and find a dropped trailer that doesn't have a king pin lock on it, crawl under it and measure the diameter of the pin with a tape measure, then compare it to the 5th wheel camper or race car trailer you want to pull with the same kind of truck/5th wheel that you would pull a commercial semi-trailer with.

 

A standard king pin is 2.00 inches in the groove. a 6 inch vernier works great to measure it.
To measure to see if you have enough clearance on the set back measure from the center of the hitch jaws, to the outer corner of the truck. If you do not have enough clearance, I would call the trailer Manufacturer and see if they have an adapter to extend the reach, or get a different truck, very few sliders on a truck will travel back past the mid point of the axles.

 

Correct and Correct, I use a standard king pin lock if I drop my trailer.

 

There's no adapter for that, just slide the 5th wheel back, if you can get it centered like mine, you should be fine.

 

Mine is 76" from the kingpin to front of trailer at the kingpin height, so I'm guessing they should be the same. If I turn my tractor, at the closest point, front of trailer to the mud flap hanger is 4 inches. When my tractor is straight to the trailer, there is 23" from the back frame of the tractor to the front of the trailer.

If you need anything else, let me know.