The RVGC-A is the adjustable king pin box for gooseneck trailer version which gives you 4" of adjustment down by the coupler and most trailer manufacturers have adjustable whole patterns to allow you an extra 3" of adjustment. Which makes the total about 7" of adjustment.
RVGC-4210A fits "Lippert" king pin box models 1716, 1116, and 0115.
PopUp gooseneck Hitch products are made in the USA.
If you want to know the location of the gooseneck trailer coupler using the new king pin box (because these king pin boxes fit several different models) below is how to calculate the location of the (top center of the gooseneck ball) coupler.
From the center of the most forward and lower bolt hole (on the king pin box of your trailer) measure forward 19-3/32” and and down 19-1/16” to 23-9/16”. This will give you the location of the center and top of your gooseneck ball with your new adjustable 5th wheel king pin box.