1. You dont need spherical bushings. The point of the spherical bushings is that they do not bind under movement like a very high WHP drag car, or a road race car will see.
2. The difference is the material, steel vs chrome moly. Chrome moly is ... either stronger, lighter, or both, i cant remember off the top of my head, but it is "Better" if you chose to spend the money.
3. How many jack stands do you have? I would suggest 4. Get the whole car in the air and supported on the pinch welds, then just place the jack under the diff enough to support the weight, not enough to actually pick it up. Have a GOOD torque wrench for this job, as some of the components need 130 ft/lbs. This means you'll have to have the car nice and high to get the leverage you need.