Ok, so if I understand correctly, you have the car body on jackstands, and lifting rear axle with floor jack at the differential pumpkin. I am also assuming that the garage floor you're working on is fairly flat and level. If that is indeed the case, you should be able to gently push the axle forward (on the side that you need to line up), and it should move. It would help if you had a second person but you should be able to move it yourself. Just be careful. If it doesn't roll easily, then get some help. Better safe than sorry.