A Long clutch in a Pantera is the wrong clutch.
It uses a diaphram, Bork&Beck type.
Although it will bolt up you will not be able to get enough clutch travel with it.
Also like LPB states, the 10.5 disc is the right choice rather then the 11 inch.
Center Force makes a dual friction unit just for the Pantera.
I got mine from Hall Pantera also. It ain't a cheap clutch but it does work very nice.
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