The 8 1/4 thread
Hope this helps.
I've done this a few times, and what I found is that there are 2 different sure grip carriers.
One of the carriers will fit the 2:45 gearsets and lower numerically, and will not fit 3:55s
You'll need a suregrip carrier that came with a 2:76 or higher numerically to fit the 3:55's etc.
If the 3:55s come with a sure-grip from a vehicle, it'll fit if the axle splines are correct. (It is possible to mount the 3:55 on the wrong carrier, buyer beware.)
Bearing sizes, axle splines vary as mentioned above.
The reluctor ring is separate and can be left out.