Here's how I lifted mine... could work for you if you have the garage space.
First I did all of the rust repair (inner & outer rockers, cab supports, rocker boxes, floors, pillar bottoms, lower side panels, etc.,etc) POR-15d and undercoated the bottom, finished the bodywork and paint... all basically with the body on the frame and the top on to keep things lined up. That part gave me four or five years to figure out how to get the frame out from underneath.
When it came time to lift the body I built a scaffold of sorts in my garage. I strapped some 4"x4" posts to the rafters, screwed cross bracing to them to stiffen it up, and then used two 2"x10"s as joists to hold up the body. I drilled a couple of sets of holes in each of the posts for the joists so I could use my cherry picker to raise / ratchet up the body in stages. I lifted the front a foot or so, then the back, then the front again. With the body in a structurally sound condition, it didn't flex a bit. If I had tried this before doing the rust repair it probably would have folded in half.
It worked great and I was able to get the body well off of the frame. I had room to roll the finished chassis back under the body with the engine and drivetrain in place on the stock wheels.