That can be a bear, the old GM shims in the frame pockets, that are added/subtracted from inside/outside each trailing arm, are how the toe in is set for either side.....
over the decades, they are mostly changed out for stainless shims....but you still have to battle the bolt, and that's all subject to rust, and so to see if the frame in that area is in good shape or not, many are NOT.....
it can turn into a battle ROYAL....mainly due to age and climate conditions.....
:hunter::club::clobbered: