In your initial post you asked "Can it be done with the body on?". We are just responding with opinions on that. Nothing negative meant by my post. Really just being honest and trying to help. I was just conveying that I first attempted with the body on the frame and the job totally sucked and the results sucked. When I first bought my Bronco I approached it as a mechanical restoration. I laid under it wire wheeling with goggles and breathing mask and then painted on chassis black. Later I realized all the body problems and started on the body. A year or so later all the chassis black had started to flake off the chassis because I just had not prepped the surface properly. I finally decided I wanted my Bronco as perfect as possible and separate body from frame.
Of course it is all up to what kind of results you are looking for. My opinion is sure you can do it with the body on the frame, but it will turn out not as good. But again, opinions are like assholes and everyone has one. I sandblasted my frame and the coating is holding up much better. But, true, mine was never and is not a daily driver. You're going to give up something either way you go I suspect.