Swapping to an 8.75 suregrip

Regarding the thrust block/buttons, which type of sure grip do you have?

Clutch or cone?

As far as DS length I would strongly suggest contacting your local driveline shop and ask them how they want you to measure and go from there. When you measure, the suspension MUST be loaded. As in jack stands under the rear so the full weight of the car is on it.