480 lbs? Wow so half the normal carrying capacity went to the bed.. nice job on it.
I have had firestone air bags on my old dodge 2500 megacab and a Tahoe, they were great on both trucks, made towing/carrying a load much better.
I think they are available for older Toyotas
http://www.sdtrucksprings.com/index....771BoCld3w_wcB

 

I believe the bed wait for a 92 Toyota pick up was originally about a 200 pounds, so it's actually like having 280 pounds in the original bed. Driving around I notice a lot more traction, and I don't notice the extra weight too much.

 

Did those take the place of the original, Rubber bumper stops? I can't tell if the top bracket replaces, or is beside the "bumper stop bracket"
Did you have to remove these, to mount your airbags?