Well, removing the bed is a big help and almost needed if you plan on drilling out the rivets.
You need to jack the back up and get the wheels just off the ground, no more than an inch. Use a jack and like 1.5' of 4x4 wood as a extension on the jack and lift it by frame. Then stack some blocks or wood to act as jack stands.
Easiest way to remove the rivets is to center punch all the rivets then use a big *** drill bit to drill off the heads. Or grind the living hell out of them. Then beat the living **** out of the shackles till they fall off.
Replace all the rivets with 1/2" grade 8 bolts. I know on my truck I had some clearance issues with the bolts, the bumper brackets that bolt to the frame get in the way a bit.
Oh, and do both. It's not worth having to go back and do the other later.
1994 | 3.0l | Auto | 4wd | Ford 8.8 with discs, Detroit Locked | Dana 35 | 4.56 gears | 5.5" suspension + 1.5" spacers + 3" body