1966valiant

I am helping a friend restore 66 Coronet and we need to know what the factory color of the underside of the floorpan was? I can see that it was black(the car is red). Just wondering if it was flat, satin or what they call a chassis black or something else?
Is there some place that I can get info on the color of other items on the car or whether it it got painted at all? If I could get a book or something, it might save me from driving you all crazy with a million questions.
We would like to keep the car the car as close to factory original as possible. He bought it new but it has sat for 30 years while he pursued other interests. It is a Coronet 440 with a 426 hemi. Only 500 built.
Thanks for any info.