8.75

The most accurate list I've seen:
An accurate 8 3/4" rear axle width list | For A Bodies Only Mopar Forum

Don't use a 7.25 rear for reference- they're different. This chart from Moparts compares them:
View attachment 1715977777
Edit: I wouldn't go by the numbers in this second chart, just posted it because however they arrived at their numbers, the 8.75 and 7.25 aren't the same. Take it for what it's worth.
The first list is accurate to every rear I've had the opportunity to personally measure.
Yeah, some of MoParts measurement are incorrect, plus they lump all the '73-6 A-body 7 1/4 rear ends together, when there are 2 different versions.