[tim dean]

Tunnelport,
Since no one else has jumped in to answer, I thought I'd tell you how I understand it. A nationally known header manufacturer recently used my '64 to fit some new style headers they were developing. As I understand it, when they fit the headers to my '64 there were clearance problems when they did a trial fit on a '68 -- something about the crossmember being wider on the '68 and the engine sitting differently. So I suppose in answer to your question, if it fits and '68 and later, it will fit a '67 and earlier, not vice versa.
Tim