Sometimes you just get lucky.

I purchased an a-body 8-3/4" axle/diff from someone for $250. I stuck it in my garage several months ago and haven't looked at it since...I didn't even know what case it was. Tonight I finally looked. It's a 489. Score! Even if it needs a rebuild it's probably worth it at this point. Next time I'll determine whether or not it has a sure-grip unit. :D

Oh, and my Mustang rear caliper mounts arrived. Maybe I can actually get something done!