Erik, Changing over a set of gears can be very frustrating & time consuming, especially if you have never done one before. If you have another complete rear end and you know it's good, I would swap over the whole thing.
There is also a way that you can change the gear set without setting up the ring & pinion . I wont guarantee it, but you might get lucky. I have done this before & it worked fine. take the entire carrier out with the ring gear & shims along with the pinion gear, shims & crush collar, & install them in your original rear end exactly the way they were in the 70 rear end.The shims need to go back in the same way they were.
You should be okay as long as the housings are the same, I'm assuming they are both 12 bolts. Also install a new pinion seal.
Or you can just use just the ring & pinion gears but they would have to be properly set up with new shims & crush collar.
A good rearend guy could do this for you if you havent done this before.
