Well... I don't know much about Ludwig drums... I own a "64 Acrolite, that I need to put back together, and a "69 marching snare... I would love to own a Ludwig kit but that's another story....
BUT maybe this will help answer the question: reading "The Ludwig Book" by Rob Cook indicates that the P-1216A in use from 1962-1965 used 1/4" bolt with 18 threads per inch. That was replaced with P-1216D that was introduced in 1965-and still in use at the publishing of the book used 5/16" bolt with 20 threads per inch. Both looked almost identical from the outside but were clearly different on the inside.
I suppose it would follow that a '67 tom would use the 5/16"x20... does that seem correct??