Not really much of a debate, the 489 is strong and will serve most any purpose well. However the 742 case has the biggest rear pinion bearing of any passenger car rearend ever. As such it can take the most load of any of the 8.75 cases. It's also the case Ma Mopar used when they commissioned the aluminum center section. It also uses shims for pinion preload from the factory instead of the crush collar (which is a weak point as it can lose it's tension) so you don't have to spend extra money for the aftermarket spacer. The only real difference is the pinion stem diameter. Since the 742 is larger than a Dana 60 (1.75 vs 1.626) I don't think there's a problem there.
Either way the 489 is a great case for high performance street and strip use. I still use a 742 aluminum case in my Scamp, which came out of my Duster. Which ran 10.60 at over 3000 pounds. Granted it's not a four speed (I broke every one of them) but I have used it for a season with a tranzbrake without ill effect.
