Differential Question

Yes, you can do what you want to do. You can use any case with any diff unit ( ie, suregrip or open ) but you must use the correct bearings for the diff and you have to use 489 case gears with a 489 case / or 741 gears in a 741 case / or 742 gears in a 742 case. I would still just pick up a used pig complete when you can.