I have a set of the Magnumforce drop spindles on my Challenger. As pointed out, you can lower the car quite a bit with the torsion bars but this affects suspension geometry. As Jim Lusk pointed out, you ARE NOT changing the load characteristics of the torsion bar, ie, you are not adding pre-load or tension to the bar, just moving the position of the LCA.
The big reason I did it though is the use of larger torsion bars. If you run stock bars lowering your car an inch or so is a piece of cake, too much more than that makes it hard to keep your alignment specs right without using offset bushings or adjustable tubular UCA's. But I upgraded to 1.12" torsion bars to improve the handling of my Challenger (these are awesome BTW!). When I put the car back on the ground I found out that the lowest I could go with the car was pretty much stock ride height. I ran out of adjustment on the torsion bar adjustors, the car just wouldn't sit any lower because of the size of the bars!
I looked at both the Fatman and Magnumforce spindles, as the latter was just recently released. The Fatman spindles are more expensive, and actually are made as separate pieces and welded together, they are a fabricated piece. While I haven't personally seen them, I have heard concerns voiced over their strength, especially in race/autocross type applications.
The Magnumforce spindles are cast pieces similar to the originals, but appear much stronger with material added in all the right places. From an engineering standpoint they look just great, better than the originals by far, and very clean and well done. They also run a little less than the fatman spindles. I can vouch for the full 2" drop as well, they work great. They also use the '73-76 spindle design, so aftermarket brakes are much easier to accomplish. I stayed mopar, but upgraded to '77 Cordoba 11 3/4" rotors. Also a noticeable difference with these. The Magnumforce spindles do use different lower ball joint bolts because of clearance (they come with the spindles), these are flush mounted allen head bolts. You'll want a socket attachment for these, since they use lock nuts and an allen wrench won't get you the torque #'s you need. The spindles also move the caliper location slightly, its pretty tight with the stainless steel lines I have, not sure how it would be on an a-body but long run I want to put some 45* ends off the caliper to clear the lines from the spindle better. I haven't tried it myself, but you can also swap the spindles side for side to put the caliper in the back, but I don't know what additional clearance issues may crop up with that since I haven't done it, although all the aftermarket calipers mount toward the rear...
Here's the spindles and the needed parts for the 11 3/4" rotor upgrade...
and some before/after of the wheel well...
and some shameless photo-whoring :-D
