Next, we noticed the lower...
Next, we noticed the lower balljoints are different. On the A spindle, the balljoint is integral to the steering arms, while the B spindle has a balljoint in the control arm, having just a tapered hole in the steering arm. The late A-Body lower balljoint is actually used in '73-'76 A-Bodies, '70-'74 E-Bodies, and '62-'72 B-Bodies. They carry Moog PN K781 for left and K783 for right. These numbers can be crossed referenced at most any local auto parts store. The late B spindles do use the same mounting holes, so the solution is to use the A-spindle balljoint. The only hang-up is the attachment bolt length. The B spindles use a shorter bolt, so you'll need to get your own bolts. Use 5/8-inch by 18TPI by 2.5-inch-long grade 8 bolts. They're readily available at any fastener store. It's best to use squish-type lock nuts as well. If you prefer the OEM bolts, you can find them on any of the above-mentioned cars using the 781/783 balljoints.
Mind you, this is not a visible condition-it's very slight, and is nearly undetectable by the average driver. It would simply feel strange or touchy, but the driver wouldn't know why. Slip Angle is also related to this, which means the car doesn't follow the exact steering angle; forward motion causes the front tires to slide a certain amount in turns, so the turning radius of the car does not match the turning radius of the wheels. Because of the slip angle, minor amounts of toe-change are largely undetectable in a street car. I say street car because a serious race effort has to account for every possible issue to gain the most performance from a combination; in this type of car, everything is important, no matter how slight.
Wider tires are also less sensitive to toe-change and a little more sensitive to camber gain, which leads us to the next topic. Negative camber gain refers to the wheel leaning in at the top as the suspension compresses. When the car is turning, it normally leans to the outside of the turn, and the outside wheel/suspension compresses. Negative camber gain allows the tire to remain flat on the road, maximizing traction, despite the car's tilted attitude. Increasing negative camber gain increases cornering abilities substantially-again, you won't feel much difference, but a stopwatch will see it.
Finally, the last major issue is roll center. It's the imaginary point by which the car will roll in a corner. It tends to have a direct relationship with the car's vertical center of gravity, which is generally up near the cam centerline of a regular V-8. The closer these two points are to each other, the more resistance the car has to rolling in a turn. However, the higher the roll center, the more chance of jacking. Jacking refers to the car rising up as it rolls, decreasing stability. This is seldom seen as a problem in 99 percent of the cars out there, as only pushing a car to its limits will cause this phenomenon. Serious road racing cars will want to avoid a high roll center. It's best to have it near the ground and use a larger anti-roll bar to resist rolling in turns. With a street car, the roll center isn't too much of an issue as the high forces that cause jacking are seldom, if ever, reached.
The Final Outcome
Overall, using the B-spindle will result in geometry changes that are unnoticeable with all but the most aggressive drivers running against a stopwatch. Even at that, there's a good argument that the increased camber gain will have a positive impact on cornering while the increased toe-in through extension will go undetected.
The last obvious items we...
The last obvious items we see are caliper location and rotor size. Some cars had the calipers mounted in the rear, while others have it in the front. Some ('76-'79 B-bodies and '79-'81 R-bodies), had 11.75-inch rotors and others 11-inch. Some cars, the '70-'74 E-Bodies and the '70-'72 B-bodies, used the weird pin-type calipers. The spindles are the same, and simply swapped from one side to the other in certain cars to provide clearance where needed. To make the swap more trouble-free, it's recommended to install them with the calipers facing as they would have in your model, which is usually to the front.
Also, use the disc brake hoses...
Also, use the disc brake hoses for your particular model so everything fits as it should. In the earlier A-Bodies, use hoses from a '73-'76 disc brake A-Body. The pre-'73 A-Bodies may also have a clearance issue between a sway bar and the bigger front-mounted calipers. It may be necessary to mount them to the rear if a big sway bar is used. When buying replacement parts, such as calipers, rotors and bearings and brake pads, use the donor car as your make and model. You may also swap between the two rotor sizes by using the correct caliper brackets.
Shown above are the two different...
Shown above are the two different brackets. The bracket for the 11-inch rotor is on the left, with 3 3/8 inches to the hole centers. The 11.75-inch bracket has 3.75 inches to the hole centers. The A and B spindles both use the same axle stub and caliper bracket mounts, so it's possible to use the A/E-Body rotors and calipers, as long as you use the shorter caliper bracket. Although all of these rotors have the bigger bolt circle, you can at least keep 14-inch wheels by using the 11-inch rotors. If you can use 15-inch wheels, step up to the 11.75-inch rotor for better stopping power.