As discussed yesterday in another thread you basically have two choices that I know of.
The first was Magnumforce.
(
http://magnumforce.com/store4/magnumforce_kmember.htm )
The trouble with their conversion is that they use the stock upper shock mount for the coil-overs. This shock mount in the inner fender was never intended to take the full weight of the car. As a result it is unsafe and I have heard of some cars collapsing on the track.
The other (and better) conversion is the AlterKtion conversion.
http://www.bigblockdart.com/alterktion/index.shtml
This is MUCH stronger and ideal for drag racing. The main advantage (and reason for development) is to make life a million times easier when it comes to fitting headers in a big block A-body.
Disadvantages are there is no provision for a front sway bar. Anyone that wants to drive a car on the public roads without a front sway bar is MAD. Drag racers like no front sway bar because the car will shift weight to the rear faster without one.
Another (but lesser) concern is that there is nothing to prevent fore and aft wheel movement. On the stock K-frame you have the two diagonal rods that locate the end of the lower control arm to the front of the k-frame? They are there for good reason.
Anyone that has driven a Mopar with worn bushes on the front of this strut knows how bad this makes the car handle. But again on a drag car this is no big deal. As long as the car does not get badly out of shape of course.
Bill's AlteKation does not flex in this way as badly as the stock set-up. In fact i would guess it would flex at least 50% less. Maybe more. However to eliminate this movement completely you would have to fit SOLID suspension bushes and that would kill the ride quality and possibly lead to some other suspension failier.
It could be that Bill has made some provision for this in his design. If he has I would love to hear about it. But looking at the detailed photographs, both on his website and the photographs of one of his kits on a freinds Dart, I can't see anything to reassure me.
Don't get me wrong. I think this is a very good kit for a mainly Drag use big block A-body. If I was building a B or RB powered Dart for track action I would use one of these kits myself. However I do like to DRIVE my cars quite fast on public roads. I also like to think that in an emergency I would be able to brake and/or steer around anything in my way. I doubt that would be the case with any of these conversions I have seen so far.
Now the next question. Why do this on a Challenger?
There is NO good reason to fit either of these kits to a Challenger. The only advantage is that they give you R&P steering. I agree that R&P steering would have a BIG advantage over the stock Mopar unit. But any advantage gained in steering response has been taken away with lack of suspension control. So you are no better off.
The kits ARE lighter than the stock set-up. But there are better and SAFER ways to loose weight IMO.