Aftermarket rear frame rails?

The rails i'm looking for are for my brother for his 71 Dart project.
He cut the spare tire well out of the trunk floor and found that the inside of the frame rails are all rotted,i said we should just back-half it and put in a 4 link but he wants to keep the leaf spring set-up.
So now were looking for aftermarket rails that we can move in a couple inches so he can run some fat tires.