I'd like to double check this, SelectAire cars may be the same length (at least I have seen several that were)
In the morning I'll try and do a bit of research.
Richard
Regarding the passenger side courtesy light bracket:
According to my version of the 1967 Electrical Assembly Manual, just the long bracket was used. Likely turned to the side a bit to miss the air conditioning box when equipped.
My version of the 1968 Electrical Assembly Manual, indicates that the long bracket was used 'without A/C'.
My research shows the driver side or 'short bracket' under dash courtesy light bracket to have a Ford part number of C0AZ-13763-A. Long bracket on the passenger side has a C7ZB-13763-A Ford part number.
Something on the unfinished list of things to get back to:
I've been working on my Select-Aire system the last few weeks & Saturday, I bumped into the evidence that seems to suggest for at least the 1967 Mustang, that
Ford intended for the Select-Aire cars to use a "Shorty" courtesy lamp bracket on the right hand side. (same as left side underdash courtesy lamp). See 1967 Mustang electrical assembly manual page 89, (E7-8655-8), bottom left of the page. (same on page 80 for the 6-cylinder cars) The assembly manual cites item #24 as a "270453 BRACKET COURTESY LAMP"
I surely cannot speak to research that suggests otherwise. As mentioned earlier, some of these "differences found" can have a lot to do with previous owners adding the option (it is very easy and very desirable).
This may not help anyone determine what they have
found on their example but hopefully it should show what Ford likely
intended to be installed. With all research I have done to date, it looks like Ford intended the longer RH bracket to be on all fastbacks & convertbles WITHOUT Select-Aire and the shorter version used on all fastbacks & convertibles WITH Select-Aire. As far as Coupes are concerned, it seems that Ford likely
intended these underdash lights as an add-on with the "Courtesy Light Group" option. The Courtesy Light Group would have included an underhood light, trunk light & glove box light AND underdash lights on ALL models. (as noted here:
https://media.ford.com/content/dam/fordmedia/North%20America/US/2013/11/18/1967_Mustang_Specs.pdf )