You can gain the radius back in two ways. You can have the box torn down and have the radius increased. It essentially has stops internally that limit the range.
Or, you can use a WJ pitman arm, which about 1-1.5" longer then a standard tj,zj, xj, etc etc.
A WJ pitman is about 45$ at the dealer last time I checked a couple of years back.
Lastly, I would be carefull in assuming that your box is the cause of the death wobble. It is more likely that your box is trashed as a result of the death wobble. I would hate to see you put in that box only to tear it up because you still have death wobble.
The best thing you could do is have someone good with death wobble look at it, and give you some recommendations.