Correct Length Pinion Snubber Bracket

I am just about ready to install my A body 8 3/4 rear end in my 1966 Barracuda. The center section does not have a pinion snubber on it so I have been looking at some that are available. There appears to be three different lengths for the bracket an 8" large, a 6" medium, and I believe the last one was a 4" small or something like that. My question is what length do I need for my Barracuda and why the different lengths? Any help and info will be appreciated.
Thanks
Bob