Just posting because no one else has. At some point they became 8.625", but I am under the impression that causes no issue with the older 8.5" carrier/housing. That's not gospel, I just recall hearing something along those lines. The housing is obviously a different casting, but I'm not sure that means the innards are not interchangeable.
I guess if you can find some vendor selling 8.5/8.625 ring/pinions interchangeably, that would be a good indication you can.
Post up with what you find.