Take caution when removing the paint off the firewall. The body series number is usually in the area around the gutter, there are a number of check marks, paint code (you already found) and the 4 digit job sequence number (it will match your build sheet) in the area behind the distributor. Most but not all were applied to the firewall prior to painting.
Leeds cars are (from my research) the only cars that used the undercoating around the heater box. Pretty ugly and messy but they used it. It is also very common to have undercoating overspray in many areas. Nice to know about the D88 mark. I don't recall seeing that on there before. Neat.
