Just so we get straight what you're telling us, does the perch [the part that is welded to the axle tube that the spring fits in] have a hole in the center? If not where is the bolt that goes through the center of the spring positioned? The lower plate that is bolted to the bottom of the springs is the shock bracket, it clamps the spring in the perch and has a place to mount the shock. The lower plate/shock bracket has a hole in it, that the center pin of the spring fits into, after the whole shebang is bolted together the lower plate holds the spring in position.
When one installs traction bars the lower plate is usually removed and replaced by the traction bar.
As for the angle, mine are 1-1/2" lower [closer to the floor] at the front of the bar than they are just ahead of the spring perches. The front of the bar is 2" below the bottom of the spring, which is good as the rubber bumper at the front of the bar is just about 2" high.

Do you have new springs?
Have you had the springs re-arched?
Are they old springs that are somewhat clapped out, not unlike mine?
I'm sure if you optained five sets of Firebird springs of various spring and load rates and tried them on your car, one set at a time, the angle of the perches would be different in between all five. I'm also quite sure the angle of the perches, in relation to horizontal, will not be the same after 40 years of thrashing than they were when first installed.