[mr48chev]

I'd think one could rig a simple latch mechanism to secure the lean back near the top so it won't go forward even if it is an additional seat belt that is anchored high behind the seat and at the bottom with the other seat belt anchors and only holds the seat it's self. At times you don't want it to show you just unlatch it and put the top belt behind the seat. Most people probably would't notice an extra belt that matched the other ones being cinched up tight against the lean back. I like the looks of that bus seat setup if the child in question is tall enough for it.

From experience it isn't the fasteners that break holding a seat or belts in a crash it is poorly installed fasteners pulling out or pulling though weak floors. That is if all the fasteners are there to hold the seat down. When I rolled my son's old 70 C10 I found out that after he had had the seat out he didn't put all the bolts back in and the seat did come loose in the crash.
There is a length of 1/4 X 2 flat bar running the width of the floor under my cab on the 48 that the seat belts fasten though mu students made sure that those belts stayed in place.