The 8" is a toothpick. Those who argue that are full of
9" =
EB (Early Bronco) rear 9" are 58" WMS to WMS. They came with either 3.54 (in the V8) or 4.11 (in the I-6)
Big bearings started to appear as early as 72, but some small bearings were used up until 74. Something else to take note of is the larger brakes. They use an 11" drum, versus the 10" in the cars. EB's always came with the 28 spline axles, 31 splines weren't available until 78 *in the big Bronco 65" axle* and pretty much all of the EB axles came with the factory L/S diff.
With the strong following of the 9" nowadays, you can get up to 35 spline axles, and there is a 40 spline version that is to be available soon (w/D60 outers from what I understand)
Sunray is pretty much the end-all-be-all when it comes to beefy 9" axles. (what I'm getting in the next few weeks

)
A new idea, finally done right. Not for the cheapskates, or the faint of heart. A high pinion 9", and no, it's not using 8.8 gears like the Currie.
True High 9"
I'll have a bone stock 9" for sale soon (from an EB) if you're in DFW, and interested, PM me. (3.54, LS, 11" drums 5 on 5-1/2 lugs) To stick it in a 'Stang, you'll need new shock mounts, and new spring perches.