[JLMounce]

On an A-body with the AFX spindle, you want to use SpeedTech's steering arm. It corrects bumpsteer and adds a good amount of akerman. You "can" use a factory arm, but you end up with some wonky bump steer on the A-body platform.

The AFX spindle has about 1" of drop built in to it, so if you're targeting a 2" drop, you want to go after springs that are a 1" lower drop. You can use any conventional spring here, it doesn't have to be the SPC spring.

In regards to using both the upper and lowers, you don't absolutely need the lower control arm, however it's beneficial to have. The SPC lower has about 2* of positive caster built into it. This does two things. It first allows you to run more positive caster without setting the adjustable uppers at a point where you're starting to lose threads in the adjusters. The second thing it does is recenters the wheel in the wheel well. By moving the ball joint position forward, you are counteracting the rearward movement of the wheel by adding positive caster in the upper control arm.

It's still possible to achieve about 5* of positive caster with just the SPC upper, but depending on the wheel and tire size, this may create rub as the tire is moved towards the rear of the car.

The lowers on my car do have a travel stop integrated into the lower arms.

Your steering box choice is fine and the corvette brakes if you go with an AFX spindle would need a 15/16" master for manual or a 1" master for power assist brakes. The disc/disc combination valve is fine for most instances.