Sure grip and 8-3/4 questions

You would want to go with a clutch type unit. They are more easily rebuilt with new clutchs if you ever need to.
The different cases will work with any housing as long as you replace it as a unit. Don't start trying to mix and match pieces from a 489 to a 742. It doesn't work.
All the stock axels had 30 splines. Some of the aftermarket units have 35 splines. This is something you should watch for.

Jack