What kind of gooseneck does it have in it now?
There are many minimum-drill options on the market for both 5th wheel and gooseneck hitches. The only holes that need to be drilled are in the sheet metal of the truck bed. All frame connections are using existing holes in the frame.
Then there is the Andersen "Ultimate" Fifth Wheel that connects to your existing gooseneck ball. It's a little different from the typical 5th wheel: It puts a raised gooseneck ball in your bed, and there is an adapter to install on the kingpin of the trailer.