340-6 Intake manifold part numbers. Original?

O.K. the 3418681 is O.E., the one with the LD6B is over the counter Edelbrock that anyone could buy, the 3418682 was a after market one that Edelbrock made but only a few and went back to the 81 part #. Not sure what that was all about but I have only seen about 3 of them.