In the first two pics you can see the 66 lower grill mounting section (greenish). It is flat all the way across and doesn't have the humps at the end. These humps are where the 67 headlight buckets attach to whereas the 66 are welded to the fender itself. In the next two of the 67 system (flat black) you can see the humps. I don't know if the 66 buckets or the signal lights would be obstructed by these or not. These lower sections are quite different in shape though.
Also I remember, slightly, a small L-bracket attached to the fender that is different on either the 66 or 67 fenders. Not sure what it was for but I'm thinking it was on the 66 to support the large signal lights that are in the grill assembly. I now recall the difference in the T-bars across the top is only some extra mounting holes drilled into the 67 (red) for attaching the headlight buckets that the 66 (greenish) did not need.
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