Shelby saw fit to do this mod on the early cars, but I'm not real sure as to how it carries over in the later models. From what I've read, its not AS necessary on the later models, as Ford had corrected some of the geometry problems in the later cars, BUT, from what I've read, it will still help the later cars to a certain degree.
Wait for more input and possibly do some outside research. Rbohm may be right regarding the thickness of the shock towers being a concern on your model. However, 65 and 66 Mustangs weren't designed with this mod in mind and the success of the mod is well known at this point and is also prevalent. Regardless, it shouldn't be a major ordeal to add additional plating/bracing at the upper control arm mount, IMHO, at the same time you relocate your upper control arms.