Sure grip and 8-3/4 questions

Thanks for the replies. I kinda figured as much on the clutch type being better but just wanted opinions from guys that know. I saw that article in Mopar Action but unfortunately right now can't afford one. I know a guy with a bunch of Mopar parts that I can do some trading with so that's why I'm after factory parts.
My main concern was if any sure grip unit from one carrier would fit in another. i.e. A unit from a 489 case fit into a 742 case. I read on another board where a guy said they were different from case to case. Another guy came back and said they weren't different so I wasn't sure who to believe.

Thanks again gents.