2 options... hold the lower arm up or unload the torsion bars. You'll need to support the knuckle assembly either way. If you don't mess with the torsion bar adjusters, the right height wont change much. Should need only minor adjustment at alignment.
To unload them means resetting the right height.
The car makes a much better holding fixture for the upper arm than anything you'll come up with at the workbench vise. So yes I screw the upper joints out and in while at the car.
Search might find 50 posts archived here about bad threads in upper arms.
The pizz poor threads on the ball joint and the arm are surely distorted over time.
Soak it with PB Blaster as well as you can and work it out slowly. Don't cross thread the reassembly.
Upper bushings... These have bolts through them with eccentric washers that change caster and camber. Where there is a lot of age and rust, getting those bolts out can be the hardest part. If you end up burning them out with a torch, you aren't the first. Reproductions are available.
If you'll search offset upper arm bushings you can get a real good idea where you should set the eccentrics initially even if not installing the offset bushings. This preset will make driving to the alignment rack doable.
Good luck
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