1976 Slant Six. Adapter Plate

I did not realize the engine was a '70's. So yes the crank has the large hole. But I bet the "nub" on the adapter is the small size. As they only used the adapter with the 67 and older engines (in 68 they went to the slant six 727 auto, and didn't need the adapter). It would probably work, though, as the bolts would most likely align it close enough.