I've not messed with the the 6AL box in the Pantera. The consensus seems to be the 8920 adapter.
I do know the instructions that come with the 6AL box explain which adapter to use when. If you no longer have those instructions, they are available on line at:
http://www.msdignition.com.
Keep in mind when reading the instructions, the electronic tach in the Pantera was originally connected to the negative terminal of the coil.
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