For purely weight reasons, I don't think it's worth it. 3 guys can easily pick any stock fleetside bed up off and put it on a dolly to work on in a body shop. The beds aren't heavy (Ok a little), just bulky....I'd be kind of surprised if you do that much work and lose more than 200 lbs.
For departure angle, you'll have to decide. The bed is not tough to work on if you can weld sheetmetal. If you can't weld sheetmetal, you'll know how by the time you are done. Buy some Bondo and try not to get any thickness over 1/8".......