Is an 8 1/4", 2.45:1 diff housing exclusive?

The Mopar bible of the 70s/80s says the same thing about the 8.25, namely that it is the ring-gear carrier that is different.......... in the 70s and 80s. In an earlier post I called the ring-gear carrier, a case. To me they are the same...... but I guess I was wrong. So from no on I will use carrier.
The carrier is different because of the thickness of the ring gear. The 2.45s (and according to RRR, so are 2.21s, and that sounds about right) are on a different carrier, from all others. Back in the day, I recall an aftermarket spacer being available, to compensate for that, but I've never messed with 8.25s, because I have always had several 8.75 systems on the go.