You're mixing your apples and oranges with your peas and squash.
Then you clarified it somewhat by defining a gooseneck ball as a B&W TurnOver Ball.
If you have a TurnOver ball installed, there are two different ways to convert to a fifth wheel hitch.
1] Convert the pinbox on the trailer to a gooseneck adapter hitch that will fit onto your TurnOver ball. That's common, but very few 5ers are engineered for the additional stress and strain the gooseneck adapter puts on the trailer frame, so the trailer manufacturers will void the trailer warranty if you do it.
2] Remove the TurnOver ball and put a B&W Companion 5er hitch in the place where the TurnOver ball fits. Works good if you don't need a slider hitch, and the trailer warranty is not affected.
The TurnOver ball plus the Companion hitch will probably cost more than simply installing a 5er hitch. The only reason to do that is if you often tow both gooseneck and 5er trailers, so you need both hitches.
But the B&W products is only one way to tow both a gooseneck and 5er with the same truck. Another way is to install an "industry standard" Reese 5er hitch, plus buy a gooseneck ball that will plug into the same bedrails used by the 5er hitch.
Reese Above-Bed Gooseneck Trailer Hitch - 25,000 lbs Reese Gooseneck RP58079