8 3/4 B to A swap

I believe the 71 to 74 is going to be 5 1/4" wider. A 68 to 70 would be the 3 1/2" wider

Your right. I have the correct chart but somehow figured wrong

To the OP. What ever rearend you use I suggest making sure the spring perches are on 43" centers. I've heard of guys spreading the springs but stop and think what your doing. Your putting all the bushings in a bind so their going to wear out a lot quicker.