Driveshaft length.....again.

Your Barracuda and 1973 Duster and Dart Sport have the same wheelbase-108" inches And in 73, they went to an 8 1/4 rear end.

So you will use the same driveshaft as a 73 340 727 Duster/ Dart Sport

That driveshaft would be part # 2996157
7260 yoke
3.25 Diameter
48.9 Length

Ain't workin' on a modified car fun ??