Not worth the work
My first F-150 when I bought it had 1 ton suspension put into it. The previous owner was a roofing company and hauled shingles in the back. Now I don't know how much those weigh, but it was a horribly stiff ride that I fixed. But it also had the 5.0 V8 bored out .060 pushing about 300lbs of torque. Not sure how much an 8 ft. bed of shingles wiegh, but I'm sure it was a lot. Now yes you could up the suspension, and get some D rated tires, but now all that strain is going to the drive shafts, and into the itty bitty tranny, and now your I6 is getting hot, and you will lose miles out of the life. You could get that truck to haul 4k in the bed, but not for long. It would just benifit you to find a cheap f-350 v8 or diesel dually and hope for the best. Hell I'm sure you could find one for around 5K or less, damn near what you would spend stiffening up the 1/2 ton and fixing it all the time. Or heres another idea...get a trailer for like 2k and pull that!!!Hey but if you do haul that much get a video and brag about it!