I think that point about the steering being centered is really important.
The Ackerman angle is the angle that is formed by drawing a line through the vertical turn axis of the suspension and the tie rod end. In the good old days of the king pin, this is easy to visualize projecting down from above. The angle points in toward the center of the rearend. If you were to draw lines through the tie rod, the king pins on the old setup, you would end up with a trapezoid, not a rectangle. Your newer suspension has the same thing. This causes the wheels to toe out on turns to compensate for the different tracking of the inner and outer wheel.
All this is leading to a comment that this angle was designed in to fit the track width and wheel base on the vehicle that the suspension came from. Once it is narrowed, as you mentioned it was, that angle needs to be changed. I don't know how one would change it other than with some type of bending.
