Sure grip and 8-3/4 questions

OK the one thing I don't have much experience with is the different sure grip units. My questions are what is best (cone type or clutch type) and what will interchange into what carriers. Can you use either the cone or clutch in any carrier (741,742,489)?? Or do certain carriers only accept certain SG units?

Right now my 68 Cuda has a 8-3/4 with a 489 case and 4:10 gears. Since the rear is all put together I don't know what type SG unit it has until I take it out. The rear is probably not original to the car cause it was a 318 2 bbl car originally.

I have located a empty 742 case which I plan on installing a SG unit and 3.23 gears in for use when cruising. I need to know what SG unit to get. Cone or Clutch.