I don't think "new" exists, they will all be "remanufactured" using used parts from cores. More than likely everything in yours is still good and if anything it probably only needs an adjustment. A rebuild is also easily accomplished on your workbench.

One thing to note, if your Dart is or was a 6 cylinder car the box will have a bushing in the steering shaft instead of a bearing and this should be swapped for a bearing which requires a different case or complicated machine work.