Pretty sure a built 9" capable of handling what the S60 can is not all that much lighter.

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

Only true comparison I have seen between the S60, the 9" and the 12 bolt.

Read it and you will be surprised at the myths floating around regarding the 9".

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.