Out of Plane walls in older home! Arg!
I’m not sure what you’re trying to accomplish here.
It’s not uncommon for a 80 year old house to have moved. Bowed out walls. Dropped in places, racking the walls, giving you out of plumb studs.
You can always level a house and correct most of this, at great expense.
If your problem is when you butt new sheetrock up to the ceiling and the edge of the rock hit’s the stud on top and hit’s nothing on the bottom, then you sister studs as needed for solid nailing.
Beyond that. I don’t understand the question.
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