NE's got the right idea - I've had some experience with both the giant balloon AND the hydraulic cylinder/hinge mount...they both suck when coupled to a factory bed.
Remove the bed entirely, trash it or sell it. Start with the frame...if it's a half-ton beef-up the truck with a 3/4 or one ton axle including the hubs and leaf springs. Junk yard for a pump and mount, replace hoses and clean the control box, Northern Hydraulics for a cylinder and weld a plate mount where needed on a cross-member over the differential, build a bed from scratch and high-side it as necessary keeping in mind the yard volume. Bearings on the axles take a load too, leaf spring additions only won't get you too far safely.
Ask Tom about how he mounted a dumper on a school bus, take that advice and reduce the figures. I love his rig, wish I had one and the determination to go about getting it together. Next project won't be tree-related, it''l be a boat stout enough to get me outta here.