I'm a lousy artist so just try to visualize this:

Make the knuckle's upper section (from the spindle c/l to the UBJ) MUCH longer. Now, at rest, the UCA has a pronounced upward tilt - the angle between the steering axis and the c/l of the UBJ and UCA pivot bushings is near zero at rest. As the suspension is rebounded, watch the huge camber change as the top of the knuckle moves out. This moves the outer tie rod end a bunch, too -- there's your bumpsteer.

As I mentioned, somebody actually took the time to measure and plot this. If I can find the file or chart I will post it here. The toe change was approx. 3X on the '73-up B knuckle vs the correct one. (On a car originally equipped with the "short" knuckle).

FYI: The reason the knuckle was made taller on the '73 Bs (and F/J/J/M/R etc) was the the UCA pivot point also had to move up, since it was now on the rubber isolated K vs. on brackets welded right to the top of the rail on the earlier design.

Minimizing bumpsteer is one of the goals we should all aim for...even if the car never sees a road course or auto-x. It contributes greatly to the "pleasure to drive" factor - one of those intangibles that makes a car a keeper!

Rick