New Axle Help

1. Are you SURE that it is a A-body 8 3/4 (with the small bolt pattern, it probably is.
You 489 case is a later piece I think. (May be original in a 69)
2. ALL 8 3/4 are 30 spline, except for aftermarket spools, and possibly Detroit lockers. (HIGHLY unlikely in your case.
3. I prefer the original style bearings, but Dr.Diffs "green bearings" are much better than the old ones that have a bad reputation. If you plan on going to disc's later, you will NEED the green bearings.
4. Ask Dr Diff (Cass).
5. Small bolt pattern use 7/16 studs, big pattern use 1/2. Do yourself a favor, have Dr put in 1/2x3 studs.
6. Depends a great deal on power of the 440, stick or auto, slicks drag radials or street tires. Without more info how you plan to use it, I won't try to answer.
I will say: 500 hp, slicks, and a four speed, I wouldn't spend a dime on a 8 3/4.
450hp, a 727, 3000 converter, and STREET tires, a 8 3/4 should last just fine.
Edit: Projectile Dart posted as I was typing (slowly). Treed again. Looks like we agree.