I just finished looking at 84 pictures of 1967 Engine Compartments, and 23 of 1968 Engine Compartments. Of those, only 7-67's and 1-68 had pictures that included the lamp housings. Of these 8, one was a 67 Dearborn, 4 were San Jose 67's, one a 67 from unknown plant, one a Metuchen 67, and one a San Jose 68.
Of this small sample, the Dearborn 67, and 3 of the 67's from San Jose had the brackets.
Also of interest is that these brackets do not show up in in either the 1967 or 68 Electrical Assembly Manuals, the 1967 or 1960-68 MPC's, the 1966-1968 TSB Index (I haven't gone through all of the 67=68 TSB's page by page yet), or any of the Special Service Letters that I have (which isn't very many). One would think that an addition like this would show up somewhere. I guess the next thing is to try to find the earliest date that these appear.
Any other ideas ?
Bob