The frames and suspension coatings are 60% gloss black(krylon semi-flat is the perfect match). The entire underbody is red oxide primer(try to find DuPont-that's who provided the original)however, it should have body color overspray around the perimeter, including into the trans tunnel, as well as the sides of the trunkwell. how much would have varied from car to car(these were painted by human beings after all!), but in the "biz", our general rule of thumb is about ten inches inboard of the outside. on a model, this is pretty easy to replicate with an airbrush. The most inaccurate thing I have seen is guys taking the chassis, laying it flat, and then fogging too much color around the edge-if you want it to look real, hold it as if it were the bottom of the car and spray coming in from the sides(as a side note, just about every car from this era had poorly painted lower rocker panels) it should just have a dusting of color- if you want it accurate. That's why we "over-restore" them, to make up for the factory's shortcomings-of which there are many.