/6 to V8 swap

Ok not sure if this is the right section but here it goes, I am swapping my 1975 Duster /6 engine, trans and rear axle. I had the old 7/14 rear axle and 904 trans, I now have an 8 3/4 rear axle set up, and a V/8 904. I am swapping the /6 k member to the V/8 K member, dont have everything mocked up yet as I am in the process, was wondering if I am going to need to swap the drive shaft? Also do I need to swap the torsion keys when switching to the V/8 bars, also what is the diff between the V8 /6 bars?
Thanks
Bryan