King pin box on a 1983 komfort 5th wheel

Hi Guys ( and girls..dont want to leave any one out )

so I have an old style king pin box on this tin can...its a short box i believe is the term. I am pulling it my Toyota Tundra SR5 .

6.5 ft bed .I just got a good deal on pullrite traditional 4100 (i believe again ) its the 18 k .

i am thinking about replacing the " short box " king pin , and wonder if there is a used one out there that would work....i still need to get a capture plate also, but dont want to buy one for this type of king pin box....i guess it would probably help if i took pics...

Thanks..and down the road i will go..eventually...