1) A 240 rear end can be removed from a boneyard car by one person. A small jack would be convenient but not essential. I did have one on hand. (Installing it again would be another matter. But, no reason to carry more into the boneyard than you need.)
2) If you don't need/want the brake parts, pointing this out may get you a better price: axle-to-axle vs. rotor-to-rotor.
3) The components may be interchangeable, in fact identical, but the fasteners may be different on your car than they are on the boneyard car: you may show up expecting 21mm and find 22mm, etc.
4) One way to make the rear end easier to handle by one person would be to pull the axle shafts, as they represent a lot of the total weight of the rear end. Be careful to drain the oil and plug-up the openings. (I was prepared to do this but found it unnecessary.)
5) A 240 rear end can be removed and re-installed without opening the hydraulic brake system, so that the brakes won't have to be bled to complete this job. The hydraulic lines can be detached from the rear end and the calipers can be suspended in place with loops of wire.
6) While you're on your back in the boneyard, any and every floor mat is your friend.
7) When folks of greater experience than you suggest that the rear end may not be the problem, and suggest that you look to a simpler solution, i.e., the drive line, you should listen to them.