1970 440 Duster Driveshaft length

I strongly suggest you get everything installed and then measure for your driveshaft.

That said, here are the 'Strange' dimensions I used (after moving the rear diff back 1/2" for tire clearance):

727 Automatic 29 Spline , Add Forged Steel 1350 Pinion Yoke: None , Measurement "A": 54.5" , Measurement "B": 1.125"