Cab, my Dart is not set up to keep air out from under it, and I am sure it has exceeded 155 mph past the stripe, never an issue with handling, never noticed anything including side winds. I have no belly pan, nothing is blocked off in the front. If you are still concerned, a chin spoiler would do the same thing and then you can keep the good looks of the 65 front The 66 rear bumper requires a different rear valance and it looks like an after thought. It also has different bolt hole spacing where the bumper brackets bolt onto the body. It also doesn't look right because it doesn't follow the body lines like a 65 bumper on a 65. By the way, I need a better front valance, if you have one to spare. Mine has taken a lot of abuse in 39 years of fun, and is pretty bent up!