I don't know why people seem to think a 9" is a good thing. Stock, they are weak. Spend a ton of money replacing all the stock parts and you still have an axle that is just as heavy as the Dana but not quite as strong.

Car Craft is a comparison between the 9", the S60 and the 12 bolt

http://www.hotrod.com/how-to/transmission-drivetrain/ccrp-0806-chevy-chevelle-rear-axle-swap/

They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.