How close to the cab should the fifth wheel be mounted? Where does the king pin get installed on the trailer? How far back does the landing gear have to be installed so it will clear the tractor tires? This PDF has scale drawings and dimensions to help you.
Click on attachment for the PDF attachment

We're changing the way we make fifth wheels. The wheel itself, (the plate) is the same cast metal one we've been using for years. The mounting plate we were using is OK but it is tricky to get the fifth wheel so it pivots easily and allows the fifth wheel to tilt back when the truck is displayed without a trailer and to fit flat against the under side of the trailer when necessary.