You're thinking of Reese type rails.
If you're near Tampa I have a set I'd give you.
I've been hauling with then since 95, great rails and hitches.
That said, on our current truck I took a chance on a turn over ball and an Andersen hitch. I'll never go back to rails or conventional rocker hitches.
Rides much better, lighter to temove, clear bed.
C2500HD ECLB, turn over ball & Andersen Ultimate hitch. 395,000 miles and counting. Stock except for LBZ mouthpiece.
41' Toy hauler @ 21K lbs.