Yes, you can swap an O/D gearset into a standard iron case, and you can swap a standard gearset into an aluminum case as well.
The input bearing has a different outer diameter, but uses the SAME inner diameter. You just have to use the proper bearings for the case you're using. O/D bearings were larger because of the aluminum case and the way the O/D gear places additional stress on the bearing. Ma Mopar "solved" the additional stress problem by using a larger OD bearing. The bearings on the aluminum case O/D's can still wear out their races in higher horsepower or high mileage scenarios though. Still, I know of more than one guy that's run them behind 440's.
You still can't mix and match gears though, the complete gearset has to be swapped to do either.
