Mehaffydr:
Many years ago I installed a twin-hydraulic-cylinder dump unit in my '58 International 3/4-ton LB 4X4 and used the original bed. I had great success with it. On one occassion I weighed it with a full load of dirt, and the load was 7,000 lbs. The dump unit dropped it with no problem. I did all the work myself, from picking up the unit in a junk yard, taking off the bed with an engine lifter, and doing all the installing, welding and hydraulic-line coupling. I know this probably isn't what you're looking for, but if I can be of any assistance, please send me a reply.