It is hard to answer your question when the floor was originally the same color as the firewall. So originally there was not a distinct line.Most of the bottom if any color was overspray. So I guess you will have to decide what looks best to you. Since you painted the underneath body color it would seem the fire wall would look better that color so there is no transition. Your not going for correctness so I would do the firewall and inner fenders the same.
Harold, Are you saying the entire floor color was painted black? My vert was top coat and not just over spray. However, my coupe looked like more black than top coat.
