Thought I'd share how I mounted my jump seat bracket using swaybar bushings.
6x 25mm bushings/brackets from eBay (~$50). Bolts/nuts/fender washers ($10)
Ground off the original mounting tabs off the original brackets. Set the brackets location by test fitting.
Benefits: diy friendly (no welding), removable, urethane adds a little comfort to the seat.
Hope this helps!