Is there a hitch adapter for a ball in the truck?

Congratulations on your "new" truck. It sounds like you may have the B&W turn over ball hitch. If that is the case, the ball can be taken out and replaced with their 5th Wheel Companion. That is a full feature 5th wheel hitch. It's what I've used for over 15 years and I feel is an excellent hitch since when you aren't using it you can remove it from the bed of the truck for full use of the truck bed with no rails interfering.

Mike

http://www.turnoverball.com/