Drive shaft?

Whilst we're on the topic, my 71 dart still has its wimpy little 7 1/4 rear end that came with the original /6. If I find (or have made) a shaft to connect this little rear end to my 440/727, will I have to start over with a new driveshaft when I put a real rear under the car? I guess put differently, will the same driveshaft work for a 440/727/7.25 and a 440/727/8.75?