Making sure the K member is within specs is the most important thing. If its straight, there's no reason that crack can't be welded up by a competent welder.
If the car pulled, its most likely some of the suspension components are bent (tie rods, center link, even control arms). You'll need to find what's bent in order to fix the pull. Its also possible that the frame itself, and not just the K member, is bent.
Here are some specs, not sure if you had a Challenger or 'Cuda. The K frame specs are the same, but the overall length is a little different.