driveshaft length question

I have a 72 Dart with a slant 6, 904, and 7 1/4 rear. I plan on swapping in a 360, 904, 8 3/4 rear into it from a 68 Dart I used to have. I may have to do this in steps. That is, swap in the rear and new leaf springs and do the rest later. Will my /6 driveshaft or the driveshaft from the 68 work for this? I'd like to be able to drive the car back and forth to the shop. It's just too busy at my buddies shop and the lot is always super crowded so I don't want to leave it there and chance damage.
Thanks for any help you can give me.
Frank