[Tom Goldman]

On stock seats, I pull up the seat uphostery and if it's a bucket, weld either a tube or piece of 2"x1/8" flat stock across the back to the outer structure.
I weld tabs to this cross piece and slot the upholstery or the plastic back to let them protrude thru.....from there I either bolt it solid to a tab on the roll bar ,or if the car needs the seat to move , I use a tube with multiple holes in it between the bar and the seat.

The only bench seat I've done was on a '63 Dodge 330, there was sufficent seat frame at the top to weld a tab for attachment to the cage.
Again ,I only do this as an added safety measure to stock seats for my customers safety.
Maybe Travis or Dave Ley can weigh in on this ,as I read the rule , the requirement in Stock reads as it only applies to aftermarket seats.