.... So my question; did they have a dealer option for a dual quad intake manifold?
Not sure if the term "dealer option" would be the correct one. No there is no listing for a Dual quad intake and carbs on any list of official options for 67 (salesman brochures, guides, list )
In general dealers would do allot of things to make a sale but the challenge IMHO that you have with a Calif car is the unlikelyhood of a dealer messing with anything replated to emission standards. Since the Mustang had never been tested and certified with that intake, carbs and air cleaners (no they couldn't just apply the tests done for the Shelby's) its my opinion that dealers would not have made this modification prior to the sale of the vehicle or even after. Instead they would be more than happy to sell you the parts and have you take it to one of the many speed shops in the area for installation/modification.
While this would have been going on it would be more likely that the buyer would simply buy an aftermarket intake and carbs rather than the Ford/Shelby stuff since it would be cheaper and at the same time strip all the Thermactor system from the car
Since modifying the car would be rewarded with fines and allot of legal mess dealers would likely choose to not make this change on a vehicle used for street usage.
If so was it the GT500 mid rise dual quad intake or a different one? Also, if it was did they remove the smog pump or incorporate it in to the dual quads?
I wasn't sure if the dual quad on a 390 would fit under the hood!
If your ever looking to show the car be aware that organizations often have limits as to how many "options" or accessories they will allow on a concours cars and its been my experience that speed related options/accessories are the least accepted of them all.
If you choose to go this route IMHO your choosing more of a Day 2 build of the car rather than a factory/as delivered car.
Don't think the whole assembly with air cleaner will clear a stock Mustang hood anyway - but then again there is the period correct teardrop hood, then the spoilers trunk lid and the 66 style quarter windows........