'70 Duster - First MOPAR Build

Tires are 245/45R17 in the front and 255/50R17 in the back.

I don't think you'd have any problem with the sway bar in any rear end. But, I'm not familiar with the 9". Are you talking Ford 9" or MOPAR 9 1/4"?

You can sort of see better here...
Firmfeel Mopar Suspension and Steering

If you go with this sway bar, do not be in a rush. Took me like 12 or 13 weeks to get it.