ETD,
To the best of my knowledge, no manufacturer is making a one piece oil pan gasket for a Big Block. Fel Pro has one for the Small Blocks, but no BB. The only exception to this is the 1991 and newer Mark 6 stly big blocks which come from the factary with a 1 pc rubber gasket. But this gasket is not usable on the older style motors, which I think is what you are looking for.
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Bill Koustenis
Advanced Automotive Machine
Waldorf Md