I have a 1973 Roadrunner that has all its original sheet metal and I recently stripped the interior to prepare it for painting. I found the buildsheet on the floor under the carpet however it is in very poor condition. I did however find a E5X9 on the X beam behind the seat but have not been able to decode it. I have checked every broadcast sheet web site and several books but it hasn't shown up. Can anyone tell me what it means?