Ok, so we must have some kind of Ehrenberg follower here.
The simple truth is that Ehrenberg was wrong about the F/M/J and 73+ B/R spindles. Which is probably why he has NEVER posted the actual geometry issues or quantified any of the claims he made regarding their use. Fortunately, someone actually DID. And you can look at all of the differences yourself, right here.
Swapping Disc-Brake Spindles - Mopar Muscle Magazine
If you look at suspension geometry plots, you should notice several things. One, the geometry changes are pretty small. Like most people won't even notice the difference small. Yes, there is a slight increase in bump steer with the FMJ spindles. However, there is also an improvement in camber gain. Everything in suspension set up is a trade off. As the Bill Reilly article points out, camber gain can be very important, and for those of us that run wider tires with more modern compounds an improvement in camber gain can be more important than a slight increase in bump steer.
And then there's the "ball joint overangling". Well, that's just BS, plain and simple. I run FMJ spindles on my Duster (and for 70k+ miles on my Challenger too, although E-body geometry is slightly different). Because I also run adjustable strut rods and do my own alignments I have cycled my suspension through its entire range of travel more times than is probably healthy and can therefore say there is no "overangling" that occurs. Certainly not on either of my cars at any rate, and I had no premature ball joint wear on my Challenger over the 70k+ miles I used it as a daily.
The FMJ spindles work great. They work especially great if you've upgraded your wheels to run wider tires with modern compounds and tread designs. And if you haven't upgraded your suspension to improve your handling, well, you probably won't notice the difference. Unfortunately, the days where even F/M/J cars can be readily found in the wrecking yards are pretty much behind us. Who knows how many people could have gotten a cheap disk brake upgrade if they hadn't listened to Ehrenberg's unsubstantiated nonsense.
Beyond that, it is a great article and has lots of good information about ID'ing parts. But yeah, unfortunately almost none of these cars are easily found in a wrecking yard, so, most would be better off buying the stuff from DoctorDiff rather than junk yard diving for parts.