71 up 2.47 to1 and 2.66 to 1

Seems 67 A body would be 26 output, and 68 up A body is 30, based on what i read on Brewers.

My car is a 71 Duster with 71 small block K, 440 using Schumacher mounts and 727 trans. What are the chances that my driveshaft will be the right length with the A833 that is going in?