The FMJ spindles are not an issue - they are a factory built part. They have been tested by Ma Mopar. The spindles are not going to disintegrate or come apart, and the issue on alignment - no issue. I took my car to the shop and did not mention a thing, they lined it up and it tracks perfect and is not wearing tires, steers and brakes like it should.
Why should it matter if "you align it yourself" in your garage, versus paying for a shop to do the same thing ???
Is that like saying that those that "restore a car themselves" are not as good as paying HUGE $$$$ to a shop to restore the car . . . I know some great mechanics that I would not say are "backyard", they could work in any shop they wanted.
If the after market builds parts, they are tested too - otherwise the lawyers will be on their heels quicker than you can say boo !
What you have to watch using the FMJ spindle, is using the correct caliper that has the bleeder screw at the top, and getting a correct brake line that can be routed correctly and not kink through out the movement. As mentioned, Dr. Diff has stainless steel line that works perfect.
The write up on BB Dart states everything perfectly . . . no issue to worry about . . . the spindles are factory, the alignment specs are factory, the brake calipers/rotors are factory. The hoses, well, they are after market which is actual UPGRADE from factory ! . . . actually, the spindles HELP with some of the alignment issues that happen to the cars over the years.
If you ONLY USE NOS/FACTORY parts for your car, because they are FACTORY and won't look at "aftermarket" parts, you sure have more $$$ to spend on your car than I do . . .