need color Info about detailing

I'm detailing under the hood of my 72 Chevelle SS conv.,the orginial color is Flame orange /whith stripes,matching number car. question is: I need to find out the color I need to go with for spraying the firewall. I've seen a lot of people would just paint it black. Does it need to be flame orange as the orginial color ? Or what type of black? Also the replacement paint for # 65 flame orange is a base coat/ clear coat, when the bodyshop mix it together, it came out as being just a hair off from matching the Orginial color. Will this hurt it ? Or is this normal ? thanks for the help, Dennis, Florence, AL.