i did mine alone. The issue isnt really needing 2 people, its the old body mounts fighting you and lots of cussing with a sawzall and many blades to get them cut.
If you just use a jack and a 2x4 you can lift the truck to slide in the mounts easy by yourself. The only hangup could be if you bought the gas filler tube extension, that a little bit of a bugger to get the screw holes lined up again with the bed by yourself. I never detached mine because the filler tube was barely long enough to not need an extension.