WOW, that's a tall question without specifying more detail:
Suggest you call Currie or Moser Engineering with the following information in hand:
1. What is the stock spring width (pin to pin)
2. What width axle do you need (flange to flange)
3. What horsepower/torque range do you have
4. Where is the car being used
5. What is the tranmission
6. Drum or discs
7. What is the car weight

They can give you a price for either an assembled axle OR a housign where you add your internals. It would be unlikey that you will find a stock Chevy axle that is a bolt-in.....you're gonna have to have welding done. Also, why not think about a 9 inch Ford axle?