INHO
The m9 (sorry no o) is the fab 9 inch ford yah I know it's a ford part but cheaper to build stronger than the 8 3/4 axel ends are better for rear disk than adding green bearings to the 83/4 gears are cheaper people know how to work on them. Did I say they are cheaper than MOPARs?.?
I used the m8.75 in my car love the design got hooked into keeping it MOPAR now I'm looking for a new spar center section the chrisler stuff is twice as much as the ford stuff when your looking at race stuff super strong center sections.
Almost all the major racing seris use the ford 9 inch NASCAR and circle track guy's& most drag racers use them.
If starting from scratch that's what I would do.
But on the other hand I've not had problems with my 83/4 and I drive it hard but I do wonder if the green bearings will fail or is it just talk I don't really know until they do if ever they do I'll fix it.
The Dana 60 is a legend icant deny that...
Tell moser what your doing and see what they say. Good luck