[JLMounce]

As HYWSTR455 suggets, that 1/4" of bump steer you have at full suspension articulation isn't a great indicator of what is happening when the vehicle is actually in motion and has it's springs and shocks installed. Depending on how the car is being used, you may only see about 4" of total travel at the wheel around the static ride height. That's where your measurements really need to take place.

What you're measuring is common for the GM SLA suspension system. In actually your measurements are pretty minimal compared to some reports I've read. Some people claim they've seen close to a full inch of toe out/in under bump/extension, especially on F-Bodies.

You posted up some Chassis Works bits that may help, but there's another thing you can look at here. If you're only at about 1.5" of caster, adding more not only helps with negative camber gain with more steering angle, but will also reduce your bumpsteer as it raises the steering arm in relation to the lower control arm...the direction you believe you need to go.

The way to achieve more positive caster from the stock control arm is through the use of an offset shaft cross-shaft. This will allow you to achieve much more positive caster in the system. THe offset shafts are going to be cheaper that the steering arms you found through Chassis Works and will start solving two issues inherent to the GM SLA, instead of just one. It's the route I would go first if you absolutely have to have stock control arms.

Then, if you're still out a bit, you can still consider the steering arm.